Sample Azure Policy rule for explicit list of allowed tag values

tag-notIn-policy-rule.json

"parameters": {
  "tagAllowedValues": { // List of allowed tag values
    "type": "Array", // An array of strings in the format like ["internal", "confidential", "restricted"]
    "metadata": {
      "displayName": "Tag allowed values",
      "description": "List of allowed options"
    }
  }
  // Other policy parameters...
},
"policyRule": {
  "if": {
    "field": "[[concat('tags[', parameters('tagName'), ']')]", // For example, 'dataProfile' as the tag name
    "notIn": "[[parameters('tagAllowedValues')]" // To validate if the tag value is in the provided list of options
  },
  "then": {
    // Some policy effect...
  }
}