I suppose it could be, since the commerce clause is also routinely cited as justification for "war on drugs" type of efforts. However, I don't think it is as clear cut as you make it. A contract executed in one state is not automatically interstate simply because the parties to the contract reside or operate in different states. It matters where the contract is executed. A contract can state things like "will be judged in an XYZ court according to XYZ law".