I am pretty sure a company cannot have their profit margin mandated in the United States. That is unconstitutional.
Rate-of-return limits and similar constructs are not new in the US, although they typically apply in particular circumstances with high public interest, e.g. utilities or insurance. The Supreme Court upheld them in many occasions.
As example, the Affordable Care Act limits profits of medical insurance at an 80/20 Medical Loss Ratio, which means only a capped 20% of the premiums can be used to cover administrative costs and profits, the remaining 80% needs to be used to pay for medical claims.
For a credit card company there is no precedent as far as I know, but I think there would be enough public interest to support a profit cap.