Don’t need to revoke a remittance. A remittance is a wire transfer. Just add a tax to all remittances going to Mexico.
Something like 6% money export tax sounds about right, and make it to all locations. They could also apply that to all the money being sent to off shore accounts in the Cayman Islands, Tobago and Switzerland. Of course the people doing that are probably also in favor of the flat tax and if not so taxed would use that as a way to avoid any taxation of income.