In User fields, add field of type: List Text with checkboxes radio button as widget

Use the Filed Permissions module so only admins can see this user field.

Download Rules and enable Rules UI

###Create a New Rule

React on: After Updating an Existing User Account

Add Condition: Data Comparison >> account-unchanged:status >> Operator: Equals DATA Value: Blocked

Add Action >> Send Mail >> Body: [user:name] was blocked because [user:field-example]

In User fields, add field of type: List Text with checkboxes radio button as widget

Use the Filed Permissions module so only admins can see this user field.

Download Rules and enable Rules UI

Create a New Rule

React on: After Updating an Existing User Account

Add Condition: Data Comparison >> account-unchanged:status >> Operator: Equals DATA Value: Blocked

Add Action >> Send Mail >> Body: [user:name] was blocked because [user:field-example]