Here we go again.

How about this: The pilots' collective bargaining agent has a contract with the airline that includes a restriction that specifies all aircraft above a certain weight or with more than a certain number of seats must be flown by those pilots if the flying is done under the code/marketing of the airline for which they fly. Further (in Delta's case) if any regional affiliate exceeds those restrictions, even under another code/fee-for-departure agreement, they may no longer fly under a regional affiliate/codeshare/fee for departure with that airline.

Not ownership of a "code." More than a vote. A contractual restriction.