They need to start AUDITING companies in exactly the same way Louis Lerner did to pre-2016 conservative PAC’s with “Freedom” in their names.
Companies using Modern Slavery need to be fined stiffly for every illegal they enslave, for each day of that enslavement:
Take the profit out of it.
Fines are just a cost of doing business with these people. Add in some jail time for the CEOs, even if only 30 days (double for each new offense) in the county lock up.
"Oh dear, just WHAT will the country club think of me?" There's also the threat of now having an arrest record.
And enforcement does not require legislation.