Legal Question in Real Estate Law in Illinois

This sounds highly irregular. If you complied with their first request then you were done and they shouldn't be able to ask for "more". Normally in a contract situation (which a lease is) one party can only ask for additional "assurances" if the other party has done something (like not pay rent on time) that could lead the other party to question whether there will be additional problems. Here you did what they asked and that should be it. Unfortunately it sounds like your landlord is not very sophisticated, and to get an attorney involved even to write them a letter saying they can't do this, will probably be more costly. Assuming the extra $50 is only additional security deposit, you might just consider giving it to them, getting a receipt showing the total security deposit including the $50 more, and a statement that this is the end of it. However, if they are demanding more rent be paid every month, that's quite another thing once you've signed a lease and done what they've asked they shouldn't be able to ask for more, and that's when I'd get an attorney involved because that could amount to a lot more money over a year! Best of luck.