You all need to organize. The bonus offering means they’re getting desperate. If you don’t get it, they get fined up to $14K/ea. $5K leaves them $9K ahead. To replace you costs even more. If they were a good employer, they’d be suing the administration, not being bullied on behalf of ole poopy pants.
If you’re on the fence, counter with $10K, full liability for side effects, insurance coverage for life at no cost if necessary to treat severe side effects, and employment guarantee until you leave. No more “at will” BS if they’re making you a guinea pig.