What they are proposing isn’t “Secession”. They aren’t trying to formally withdraw from the United States.
Secondly, why would Congress need to get involved? If the states want to do some re-arranging of their borders, why not? It would seem to me if this were something they wanted to do, they would have no problem with it.
Ultimately I think this is a reflection or a legacy on the Reynolds case decided by the supreme court - less populated counties or rural areas have had no defense against the large city centers for some time now.
Or put another way, what did you guys think would happen??
Secondly, why would Congress need to get involved?