My wife is the lawyer, not me, but what I know is this:
Collusion is basically when two or more businesses work together to
alienate a third party and that action causes him financial harm. I think
it is considered an antitrust issue, I believe that it can be a civil
problem too I think the idea behind the laws it that it is suppose to help
to keep the market "free" so groups ban together and take unfair advantage
of the newbie. The Federal Trade Commission is responsible to handle the
big cases, but the Attorney General can bring a case against small business
on the State level, if it really wanted to and only if there was a
complaint. Without a complaint they simply don't act.
Blacks Law Dictionary calls Tacit Collusion "a strategy where two or more
companies agree on a policy that is not put into writing." There is an
intent to deceive and harm a third party.
I don't know the history of the laws, but it would make for google
search. I'm sure there is a lot more to collusion than I am aware of. And
it is probably never going to happen, but it is always safer to stay on the
right side of the law, and to prevent potential loss.
Hope that helps.