At least in the U.S., I've never heard "violate an act." If you're using the term "act," you're generally going to mention the actual name of the law: "That violates the War Powers Act," or something like that. Unless you give the specific name, you'd just say "violate the law." I hope that helps!

I agree with the others that "law" and "act" are synonyms that can be used interchangeably. However, there's one difference. "Act" is both a noun and a verb, whereas "law" is not. So, a criminal can "act in violation of a law" or "commit an act in violation of a law". He can even "act in violation of an act" or "commit an act in violation of an act", sentences in which "act" has two different meanings.

You can violate an act, but that is the same as violating a law which is an act of parliament ( a law passed by parliament). So an act is a statute/law/legal provision. So you are quite correct when you say committing an infraction in an act ( in a law by going against the specific legal provision). You can also violate principles,a situation, a place, a person, ethics

If by "act" you mean "act of parliament" (as we would say in the UK), then it would work, but you would need to say "act of parliament" rather than just "act" ... and I would suggest it is something you would only use with, for instance, a government minister. Most people just violate laws created by acts of parliament. If you mean "act" in any other sense then I don't think you could say, "violate an act".