Here's a hypothetical situation:
Farmer Giles and Farmer Jones both supply a 3rd party chain of shops with cheese "Cheese 4 U". "Cheese 4 U" sells cheese from multiple farmers. Farmers Giles and Jones also have their own chains of farm cheese shops, from which they sell their own cheese exclusively. Competition in the cheese market is healthy.
Both farmers open up a channel of communication: "Hey, if we both agree to stop supplying our competitor with cheese, they'll have no choice but to close, and we can carve up their cheese re-selling business between us."
"Hey, that does sound like a great idea. Isn't it anti-competitive though?"
"Don't worry. We'll pull the plug on cheese supply first, then give it a couple of months and you can pull your supply of cheese. You can state that due to certain factors (obviously contributed to by our cessation of cheese supply, but you be creative there) you're also ceasing cheese supply to the company.
It'll have no choice but to go belly up and we can move in for the kill!! The high-street cheese market will be ours for the taking and we can get rid of our competitor in the cheese supply market."
"What about the competition watchdog?"
"Don't worry about them, this will totally go under the radar. Nobody likes them anyway! It's a fool-proof plan! Do you fancy some cheese-on-toast?"