A normal DMCA takedown request is taken under penalty of perjury (sadly, a lot of the big common carriers, like Youtube, have gentleman's agreements with Big Me

A normal DMCA takedown request is taken under penalty of perjury (sadly, a lot of the big common carriers, like Youtube, have gentleman's agreements with Big Media, so they don't rely on formal DMCA takedowns), and knowingly and falsely claiming to be the copyright holder is likely an infringement of the author's moral rights, which is at the criminal end of copyright law, so that's two flavours of illegal right there.