condo rental fee

That is absolutely crazy. Those who vote to pass this should just live in a coop instead. The whole thing is so reversed.

all investors get together and vote a new board in, then revoke the stupidity.

They abused democracy.
Like you said, they may increase the fee even higher in the future. Effectively stripping your right to lease out YOUR property. Being an investor is just one of the many sub groups within a building. What can be done to stop them from using "fees" as a weapon to target any groups that they don't like.
Do they need to justify that amount that renters are costing them that much to operate? It has to be reasonable. Otherwise, the fee is like a penalty for you doing nothing wrong, which should not be allowed.
May be you can organize with other investors to hire an auditor to audit the 3X proposed fee they requested.

thanks for the responses. I'm in contact with a fellow investor and we're trying to get in touch with others. There was talk at the last building meeting that some renters were being noisier/messier than the typical owner. But, no, there's nothing to justify that my renters make $ 3 months' worth of extra garbage/noise than an owner-resident.

what are your common charges?

Fight their fees with your "fees". Make a deal with your renter that he's paying not $1500 in rent, but $500 in common charges, $990 in "contract renewal and confirmation fees", and $10 in "rent". Then you write the board a check for $30 every year and everyone's happy.

Wait, is that legal? ^_^