I have it in my contract that my footer link is not to be removed without my permission. Client didn't ask and removed it. I have nicely sent him an email stating that it is against what he signed in the contract and to restore the link ASAP.

If he doesn't respond/comply what are my options here? He has not been a very good client and this puts the icing on the cake.

Myself, client and hosting are in the US.