The original pricing didn't break any US regulations. Of course, anyone can bring anyone else to court for any reason, but if the defendant didn't break any regulations, the plaintiff won't prevail, and publicly asserting that the defendant did so, when contrary to evidence, could leave the plaintiff liable for defamation.
It's also an awful place to start from, as a good-faith effort to settle the matter is much cheaper for both sides, and the only way to prevail when no regulations were violated.
There doesn’t have to be a statute that says “ you can’t raise your price more than x %” . That’s what common law means. The judge determines whether the contract between them was upheld in good faith.
Now if the contract says “every 5 years we may raise the price by 10000% “, there is good faith between the two parties.
If the contract says “every year we may increase the price by a reasonable amount to cover increasing operating cost” – the judge decides what a reasonable amount is.
That’s what common law means. The statutes are not the law. Judgements are the law.
It's also an awful place to start from, as a good-faith effort to settle the matter is much cheaper for both sides, and the only way to prevail when no regulations were violated.