It is only collusion if they get together and decide to do this. If they without working together insist on it individually it is not collusion.
It would be like 2 fast food restaurants not trying to cut prices below the other one. As long as they did not get together to make the decision it is a business practice. If they both decide not to compete with each other independent of each other, it is their business decision and illegal.
I remember an article in the paper in Colorado in the '90s during one of the gas spikes. They were interviewing the owner of the largest distributor in the area. He was quoted as saying that they had a conference call every morning and each of the distributors would announce what their price would be for the day. Sometimes, when one owner was out of line, he might adjust his price, but since nobody was telling him what to charge, the state didn't consider it price fixing. End result was that the price didn't vary by as much as a penny at any station of any brand in the region. And the state endorsed it.