As I understand the law, the mechanical license is mandatory if the song has ever been released to the public on record. The copyright holder can't stop anyone from recording and releasing it, he/she/it can only demand the statutory royalty.

Caveat: I am a lawyer. I'm not an intellectual property lawyer.

And I don't know what the proper procedure is if the license is refused. It certainly isn't worth while suing to force the issuance of the license.

P.