this is unusual because you got a w-2 and generally, all compensation should have been reported on the w-2. With a 1099-NEC in addition to income taxes on this income, you'll have to pay about 15% in self-employment taxes. This may be an improper attempt by the employer to avoid penalties for late payment of taxes that should have been withheld and their share of the FICA and Medicare taxes by making you responsible.
As for getting the employer to pay, that's up to them. There's nothing in the tax law about this except for a small penalty for filing the 1099 late
