If you have a contract that says you will pay rent plus a percentage for the space, then that is your contract. If you don't like it, go somewhere else.
As a tax matter, the 10% you pay off the top is one of your deductible business expenses along with the regular rent.
That is a legal or contractual question, not an income tax one. We cannot answer legal questions here.
. . . Furthermore, that would be a question of state law, not federal, so the answer might depend on what state you are in. You should consult a local lawyer who specializes in business law.
If you have a contract that says you will pay rent plus a percentage for the space, then that is your contract. If you don't like it, go somewhere else.
As a tax matter, the 10% you pay off the top is one of your deductible business expenses along with the regular rent.