As a private company, as long as they are not a monopoly or a quasi monopoly(), they can do what they want, no restriction.

() My personnal definition is a minimum of 4-6 participant in any market with at least 5%-10% share each (Exemple : France has some of the lowest mobile telephony fares in the world, because there are 4 "biggish" providers (one is over 50%), and they are often trying to merge "to regain pricing power", luckilly they have so far failed. 3 can somewhat manage a cartel, 4 seems to be much harder.).