diff --git a/docs/reference/workflows.md b/docs/reference/workflows.md
index e7e921e1e9..b06ae93f88 100644
--- a/docs/reference/workflows.md
+++ b/docs/reference/workflows.md
@@ -193,6 +193,14 @@ steps:
       args: "{{ inputs.spec }}"
 ```
 
+Workflows that include any `type: shell` step must also declare:
+
+```yaml
+requires:
+  permissions:
+    shell: true
+```
+
 This produces the following execution flow:
 
 ```mermaid
diff --git a/src/specify_cli/workflows/engine.py b/src/specify_cli/workflows/engine.py
index d6a73bbeb0..6769552043 100644
--- a/src/specify_cli/workflows/engine.py
+++ b/src/specify_cli/workflows/engine.py
@@ -47,8 +47,8 @@ def __init__(self, data: dict[str, Any], source_path: Path | None = None) -> Non
         if not isinstance(self.default_options, dict):
             self.default_options = {}
 
-        # Requirements (declared but not yet enforced at runtime;
-        # enforcement is a planned enhancement)
+        # Requirements declared by the workflow. Some permissions are enforced
+        # during validation and execution.
         self.requires: dict[str, Any] = data.get("requires", {})
 
         # Inputs
@@ -128,6 +128,10 @@ def validate_workflow(definition: WorkflowDefinition) -> list[str]:
             f"semantic versioning (expected X.Y.Z)."
         )
 
+    # -- Requirements -----------------------------------------------------
+    if not isinstance(definition.requires, dict):
+        errors.append("'requires' must be a mapping (or omitted).")
+
     # -- Inputs -----------------------------------------------------------
     if not isinstance(definition.inputs, dict):
         errors.append("'inputs' must be a mapping (or omitted).")
@@ -150,12 +154,68 @@ def validate_workflow(definition: WorkflowDefinition) -> list[str]:
     if not definition.steps:
         errors.append("Workflow has no steps defined.")
 
+    errors.extend(_validate_shell_permissions(definition))
+
     seen_ids: set[str] = set()
     _validate_steps(definition.steps, seen_ids, errors)
 
     return errors
 
 
+def _validate_shell_permissions(definition: WorkflowDefinition) -> list[str]:
+    """Validate explicit opt-in for workflows that run shell commands."""
+    if not _workflow_uses_shell(definition.steps):
+        return []
+    if _allows_shell_steps(definition.requires):
+        return []
+    return [
+        "Workflow uses shell steps but must declare "
+        "'requires.permissions.shell: true' before shell commands can run."
+    ]
+
+
+def _allows_shell_steps(requires: Any) -> bool:
+    """Return whether the workflow explicitly opts into shell execution."""
+    if not isinstance(requires, dict):
+        return False
+    permissions = requires.get("permissions")
+    if not isinstance(permissions, dict):
+        return False
+    return permissions.get("shell") is True
+
+
+def _workflow_uses_shell(steps: Any) -> bool:
+    """Return True when any top-level or nested step has type 'shell'."""
+    if not isinstance(steps, list):
+        return False
+
+    for step_config in steps:
+        if not isinstance(step_config, dict):
+            continue
+
+        if step_config.get("type", "command") == "shell":
+            return True
+
+        for nested_key in ("then", "else", "steps"):
+            if _workflow_uses_shell(step_config.get(nested_key)):
+                return True
+
+        cases = step_config.get("cases")
+        if isinstance(cases, dict):
+            for case_steps in cases.values():
+                if _workflow_uses_shell(case_steps):
+                    return True
+
+        if _workflow_uses_shell(step_config.get("default")):
+            return True
+
+        fan_step = step_config.get("step")
+        if isinstance(fan_step, dict) and _workflow_uses_shell([fan_step]):
+            return True
+
+    return False
+
+
 def _validate_steps(
     steps: list[dict[str, Any]],
     seen_ids: set[str],
@@ -400,6 +460,10 @@ def execute(
         """
         from . import STEP_REGISTRY
 
+        shell_permission_errors = _validate_shell_permissions(definition)
+        if shell_permission_errors:
+            raise ValueError(shell_permission_errors[0])
+
         state = RunState(
             run_id=run_id,
             workflow_id=definition.id,
diff --git a/tests/test_workflows.py b/tests/test_workflows.py
index 4c042fc7d5..7fa6a1b7c0 100644
--- a/tests/test_workflows.py
+++ b/tests/test_workflows.py
@@ -1283,6 +1283,61 @@ def test_invalid_step_type(self):
         errors = validate_workflow(definition)
         assert any("invalid type" in e.lower() for e in errors)
 
+    def test_shell_step_requires_explicit_permission(self):
+        from specify_cli.workflows.engine import WorkflowDefinition, validate_workflow
+
+        definition = WorkflowDefinition.from_string("""
+workflow:
+  id: "test"
+  name: "Test"
+  version: "1.0.0"
+steps:
+  - id: run-tests
+    type: shell
+    run: "pytest"
+""")
+        errors = validate_workflow(definition)
+        assert any("requires.permissions.shell: true" in e for e in errors)
+
+    def test_shell_step_with_permission_is_valid(self):
+        from specify_cli.workflows.engine import WorkflowDefinition, validate_workflow
+
+        definition = WorkflowDefinition.from_string("""
+workflow:
+  id: "test"
+  name: "Test"
+  version: "1.0.0"
+requires:
+  permissions:
+    shell: true
+steps:
+  - id: run-tests
+    type: shell
+    run: "pytest"
+""")
+        errors = validate_workflow(definition)
+        assert errors == []
+
+    def test_nested_shell_step_requires_explicit_permission(self):
+        from specify_cli.workflows.engine import WorkflowDefinition, validate_workflow
+
+        definition = WorkflowDefinition.from_string("""
+workflow:
+  id: "test"
+  name: "Test"
+  version: "1.0.0"
+steps:
+  - id: branch
+    type: if
+    condition: "{{ true }}"
+    then:
+      - id: run-tests
+        type: shell
+        run: "pytest"
+""")
+        errors = validate_workflow(definition)
+        assert any("requires.permissions.shell: true" in e for e in errors)
+
     def test_nested_step_validation(self):
         from specify_cli.workflows.engine import WorkflowDefinition, validate_workflow
 
@@ -1392,6 +1447,9 @@ def test_execute_with_gate_pauses(self, project_dir):
   id: "gated"
   name: "Gated"
   version: "1.0.0"
+requires:
+  permissions:
+    shell: true
 steps:
   - id: step-one
     type: shell
@@ -1423,6 +1481,9 @@ def test_execute_with_shell_step(self, project_dir):
   id: "shell-test"
   name: "Shell Test"
   version: "1.0.0"
+requires:
+  permissions:
+    shell: true
 steps:
   - id: echo
     type: shell
@@ -1435,6 +1496,26 @@ def test_execute_with_shell_step(self, project_dir):
         assert state.status == RunStatus.COMPLETED
         assert "workflow-output" in state.step_results["echo"]["output"]["stdout"]
 
+    def test_execute_shell_without_permission_raises(self, project_dir):
+        from specify_cli.workflows.engine import WorkflowEngine, WorkflowDefinition
+
+        yaml_str = """
+schema_version: "1.0"
+workflow:
+  id: "shell-test"
+  name: "Shell Test"
+  version: "1.0.0"
+steps:
+  - id: echo
+    type: shell
+    run: "echo workflow-output"
+"""
+        definition = WorkflowDefinition.from_string(yaml_str)
+        engine = WorkflowEngine(project_dir)
+
+        with pytest.raises(ValueError, match="requires.permissions.shell: true"):
+            engine.execute(definition)
+
     def test_execute_with_if_then(self, project_dir):
         from specify_cli.workflows.engine import WorkflowEngine, WorkflowDefinition
         from specify_cli.workflows.base import RunStatus
@@ -1445,6 +1526,9 @@ def test_execute_with_if_then(self, project_dir):
   id: "branching"
   name: "Branching"
   version: "1.0.0"
+requires:
+  permissions:
+    shell: true
 inputs:
   scope:
     type: string
@@ -1569,6 +1653,9 @@ def test_list_after_execution(self, project_dir):
   id: "list-test"
   name: "List Test"
   version: "1.0.0"
+requires:
+  permissions:
+    shell: true
 steps:
   - id: step-one
     type: shell
@@ -1767,6 +1854,9 @@ def test_full_sequential_workflow(self, project_dir):
   name: "E2E Test"
   version: "1.0.0"
   integration: claude
+requires:
+  permissions:
+    shell: true
 inputs:
   feature:
     type: string
@@ -1814,6 +1904,9 @@ def test_switch_workflow(self, project_dir):
   id: "switch-test"
   name: "Switch Test"
   version: "1.0.0"
+requires:
+  permissions:
+    shell: true
 inputs:
   action:
     type: string
diff --git a/workflows/PUBLISHING.md b/workflows/PUBLISHING.md
index ce0d251826..5df90dcd81 100644
--- a/workflows/PUBLISHING.md
+++ b/workflows/PUBLISHING.md
@@ -84,6 +84,14 @@ steps:
     on_reject: abort
 ```
 
+If your workflow contains any `type: shell` step, it must also opt in explicitly:
+
+```yaml
+requires:
+  permissions:
+    shell: true
+```
+
 **Validation Checklist**:
 
 - ✅ `id` is lowercase alphanumeric with hyphens (single-character IDs are allowed)
@@ -91,6 +99,7 @@ steps:
 - ✅ `description` is concise
 - ✅ All step IDs are unique
 - ✅ Step types are valid: `command`, `prompt`, `shell`, `gate`, `if`, `switch`, `while`, `do-while`, `fan-out`, `fan-in`
+- ✅ Shell steps are explicitly enabled with `requires.permissions.shell: true`
 - ✅ Required fields present per step type (e.g., `condition` for `if`, `expression` for `switch`)
 - ✅ Input types are valid: `string`, `number`, `boolean`
 - ✅ Step IDs do not contain `:` (reserved for engine-generated nested IDs like `parentId:childId`)
diff --git a/workflows/README.md b/workflows/README.md
index 31f736ff76..cd494a1bda 100644
--- a/workflows/README.md
+++ b/workflows/README.md
@@ -106,9 +106,15 @@ Send an arbitrary inline prompt to an integration CLI (no command file needed):
 
 ### Shell Steps
 
-Run a shell command and capture output:
+Run a shell command and capture output. Workflows that contain shell steps
+must opt in explicitly at the top level:
 
 ```yaml
+requires:
+  permissions:
+    shell: true
+
+steps:
 - id: run-tests
   type: shell
   run: "cd {{ inputs.project_dir }} && npm test"