An accusation against you to ACM should have details stating what you are accused of. If not, then ACM should reject the accusations. If yes, ACM should tell you what you are accused of. If someone accuses you of something that they know you haven't done (like being in violation of a patent that doesn't exist), that might be libel, and you'd need a lawyer.
If I had a patent application and it was still pending, I believe it is legally fine for you to violate the patent now, but it would be risky, because once the patent is accepted, you would be in trouble. Now I might believe that violating the patent is illegal while it is still pending, and I might accuse you of doing something that I reasonably believe is illegal, and then making the accusation would be wrong but legal. If I haven't even applied for the patent, that's different.
Now if I accuse you legally, and then refuse to provide any evidence, that doesn't make the accusation illegal, but it makes it very weak. For example ACM should reject such an accusation, even if it was true (because they cannot know whether it is true or not). If you sued me for libel, and I still refused to show the evidence, the judge would be allowed to conclude that the evidence doesn't exist and judge against me in the libel case.
PS. The question you see is only vaguely related to the one I replied to.
Should not there be negative consequences for filling complaints without having the information to back them up, to prevent people from filling complaints at random?
– J..y B..y Dec 24 '22 at 07:31