PITTSBURGH – The maker of Zippo lighters is turning up the heat on knockoffs of the distinctively shaped – and trademarked – lighters.

For the first time since obtaining trademark registration of the slightly rounded rectangular shape four years ago, Zippo Manufacturing Co. has filed a complaint with the U.S. International Trade Commission to stop the manufacture and sale of knockoffs, said Jeff Duke, the company’s attorney.

The ITC is investigating Zippo’s complaint, which was filed in May. An evidentiary hearing before an administrative law judge is scheduled for Feb. 5, but Duke said he hopes the complaint can be resolved before then.

The complaint seeks to bar imports of knockoffs. Four Chinese companies and three U.S. distributors are listed as respondents, but Duke said there are “dozens upon dozens.”

Duke said knockoffs persist, despite the trademark. “It has declined, but it has not declined as significantly or as fast as we wanted to, which is why we brought the ITC action,” Duke said Wednesday.

By even a conservative estimate, knockoffs consume 30 percent of Zippo’s business, he said.

Zippo, founded in 1932, makes between 12 million and 14 million lighters a year. Several million fans collect the thousands of designs it has offered over the years.