Conditionally drop labels

I would like to drop a label but only from a specific series. From the doc I can see that the action needed is labeldrop.

My starting point is something like

    - action: replace
      source_labels: [__name__, url_rule]
      regex: 'test_.+;(.+)'
      target_label: path
    - action: labeldrop
      regex: 'url_rule'

How can I ensure that the second action will only drop the url_rule label from metrics starting by test_ (like in the first action)?