That act (verb/adjective) would be “collusion”, “fixing” (like prices), etc., and the companies called a cartel (noun). It is anti-competitive behavior because

That act (verb/adjective) would be “collusion”, “fixing” (like prices), etc., and the companies called a cartel (noun). It is anti-competitive behavior because it reduces or eliminates free market competition, and is illegal (or at least subject to government scrutiny) in most countries.