How about a new law that says that any and all insurance policies are null and void if the insured party turns out to be in the country illegally. No refunds.
Right, more laws to cover things which are not the governments business.
How about instead the free market? The insurance companies just add into the contract, "claims made by persons who are not US Citizens, or legal residents are considered fraudulent, so will not be paid."
The unintended consequences is that the employer can get sued by the injured illegals lawyer. So the threat of a lawsuit, or the cost of defending against the lawsuit, makes the employer pay for the medical care, which means he is paying twice for the insurance.