Legacy id #'s on claims

I have a work comp. ins. co. that is still insisting that the old legacy provider ID number be on the claim. This is in addition to the individual NPI #, group NPI # and Tax ID#. Any claim sent without all these numbers is rejected.
Can they still do this?
I thought that when NPI became mandatory, that all insurance companies had to comply. Did I miss something that allows an insurance company to still require the old numbers on claims.?