You don’t need to call off on an N/S day. You don’t need to provide documentation for a N/S day. You don’t need to fill out a 3971 for a N/S day. M-00489; “A nonscheduled day would not be counted in determining when the employee must provide documentation in order to be granted approved leave” File a grievance for even being asked to provide documentation. Ask for a steward. If they then discipline for “failure to follow instructions” of not coming in on your N/S day, then good now the burden of proof is on them to prove you were available and healthy enough to perform your duties, but chose not to. Good luck with that. Not to mention all the other just cause provisions. You should also know if a carrier claims illness but is witnessed in public by a supervisor or posts photos/videos to social media it can be bad for their case. If you suffered financial loss due to being mandated on an N/S day the Union can also grieve to get that reimbursed such as ball-game tickets you can’t go to, or hotel, doctor’s cancellation fees, etc.