letter from the biggest federal employee union: "AFGE members have concluded that a widespread government shutdown has been underway since January 20 and will continue to spread whether senators vote yes or no on HR 1968"

So they might as well vote NO;
to stop from endorsing what is happening and
to not give it legal cover.
it is better this come to a head sooner rather than later, to either force trump to stop doing this or for everyone to know this is the new normal
https://talkingpointsmemo.com/edblog/biggest-federal-employee-unions-says-shutdown-is-preferable-to-elon-trump-cr