Yes they can. Quite easily actually.

They can't circumvent scope and merger/fragmentation language in a CBA. DL and NW's scope and merger language mandated an eventual merger with arbitration if it couldn't be agreed upon.

If you are attempting to drag AT into this, they were operating under a vastly inferior NPA contract that wasn't nearly as strong. That was what enabled the end result and what provided the leverage of uncertainty that was used against the AT pilots. But to imply management holds all the cards and can always do whatever they want is completely false.