The Justice Department is suing a Houston-based company it accuses of illegally discharging oil from a platform in the Gulf of Mexico.

The lawsuit filed Monday in New Orleans against ATP Oil & Gas Corp. says the company's alleged federal Clean Water Act violations were discovered during an Interior Department inspection last year.

The lawsuit claims ATP failed to properly operate and maintain the wastewater treatment system on its floating platform. That caused oil to be discharged into the Gulf in greater quantities than it was permitted. Platform workers also are accused of using an unauthorized dispersant to mask the oil sheen on the water's surface.

ATP filed for bankruptcy in August. ATP Infrastructure Partners, a company formed by ATP and GE Energy Financial Services, also is a defendant.