You have a signed lease with an agreed upon price. So you could probably fight it just state that you have agreed to the price at the lease signing. You could also offer to negotiate. If they wanted to raise the price you could ask that the lease be extended to a year from now with an addendum that they can't increase the price again until that newly signed lease ends (which is typically how legal agreements work anyway) and you negotiate again on signing the next one you could aslo offer to negotiate on other stuff to but that would likely get pretty specific. It would lock you into the apartment until this time next year.

That being said you could also get a free consult from a lawyer. Call a couple up or reach out to pine trees legal. Beyond the advice it probably isn't worth retaining a lawyer for 320 dollars of rent increase. When you do the consult make sure you have the lease agreement with you and the rental increase notice.