It depends on the situation , if you have damaged the apt or left unpaid rent then they can , and if you broke your lease before it was up they can with hold the deposit , however if none of the above is the case then I would go over your lease with a fine tooth comb , and if you still can't find a hidden clause talk to an attorney.
If there is just cause, a management company can refuse to authorize the return of a security deposit. They should put in writing the reasons it is not being refunded. Get out your lease and make sure you are in compliance.
Yes, they can in reason.
Depending on your state laws the management company can keep your security deposit if you break your lease, move out without giving a 30 day notice (even if your lease is up) or damage the apartment. In the case of damage to the apartment they must give you a written list of damages within a certain period of time (usually within 10 days of you moving out). Read your lease and check the web for "renters rights" and include your state in the search. If you've done everything right - fulfilled your lease term, given a 30 day notice and left the apartment clean and they have kept your deposit illegally some states make the mgt. Company give you back 3 times your deposit.