There are two ways to fight them. The risky way is to not pay the increase. This is risky because you can be taken to eviction court for paying as little as a dollar under, and eviction court is not a friendly place. You may well lose, and having an eviction on your record is worse than bankruptcy - it tends to follow you like the plague and make it very hard to rent again. The less risky way to fight a retaliatory rent increase is to pay it, but send it along with a letter arguing that you don't agree that you owe it, and then sue in small claims court to get it back.
Small claims is much friendlier than eviction court.
No attorneys are allowed and if you lose, there are no horrible repercussions. Members can call the Members-Only Line.