(a) The tenant may not withhold payment of any portion of the last month's rent on grounds that the security deposit is security for unpaid rent.
(b) A tenant who violates this section is presumed to have acted in bad faith. A tenant who in bad faith violates this section is liable to the landlord for an amount equal to three times the rent wrongfully withheld and the landlord's reasonable attorney's fees in a suit to recover the rent.
Official text of the Texas Property Code as published by the Texas Legislative Council.