This is true, but it actually has to be unconscionable, as in significantly above fair market rental value. If you were under paying for a long time, they can raise to fair market value in a town with no rent control, even if it's a large increase. From there, you'll just be fighting in court with the landlord (or their lawyers) which will suck up enough time and energy that you might as well move. Especially as on a month to month, if you decide to sue for unconscionable increase, they can just terminate your lease and give you the 30-90 days to leave depending on the lease.