Do you get barred from re-enlistment if you decline orders?

People get terms mixed up. If your NCO declines the orders he has to sign a declination statement. It's not a bar feom reenlistment, and it's not a flag, but they will be ineligible to reenlist and have their promotable status removed if they have it.

Of course, yesterday the Army announced that during COVID people who have signed a declination will be eligible to extend or reenlist, so that's going to be interesting to see how it plays out.

A bar from reenlistment is initiated by the CDR, and approved by the BC as a punitive action against the Soldier. It gives a 9K reenlistment code.
A declination statement is initiated by the Soldier in response to being placed on assignment and needing to meet an SRR. The request to lift it has to be signed by the O6, and HRC decides whether or not to approve it. When they do approve it the SM must immediately reenlist Regular Army for four years. It gives a 9Q reenlistment code

When I was in Germany, I declined orders to FT Riley. IOT decline those orders, I had to sign a Declination of Orders statement and self barred myself from reenlisting. But that was many years ago. Perhaps SFC (Join to see) could answer this one better.

Last I knew, he will be barred from reenlisting. Depending on how much time he or she has in, its a tough decision to make. But it is called selfless service for a reason.