The New Orleans Police Department retaliated against a former detective who had lodged a complaint against the department over alleged labor violations, the city’s Civil Service Commission found Monday. It said the NOPD retaliated by suspending the officer for leaving work early one day, thus blocking him from a promotion.

Chad Perez, a 14-year veteran who left the force in 2013, was handed a one-day suspension for leaving an hour before his shift ended Aug. 18, 2011, just nine days after he filed a complaint with the U.S. Department of Labor and the NOPD’s Public Integrity Bureau.

Perez alleged that the department failed to properly compensate officers who worked past their assigned hours, whether in overtime pay or extra time off. He called out his immediate supervisors as part of a complaint that would become a federal class-action lawsuit, which remains pending.

Perez admitted he left early that day, saying the window of his personal vehicle was stuck open and rain was on the way. His supervisor reached him and Perez offered to return to work but was not asked to do so, he said.

PIB investigators found the department had failed to substantiate the allegation against Perez, but by the time the issue reached then-Superintendent Ronal Serpas, Perez was handed a one-day suspension that thwarted his shot at becoming sergeant.

In a six-page ruling, three civil service commissioners found “by a preponderance of the evidence that the disciplinary action against (Perez) was motivated by retaliation.”

The commission said the NOPD never offered evidence that Perez’s suspension was in line with the discipline other officers received for similar offenses. The commission also cited testimony from then-Deputy Superintendent Darryl Albert describing Perez as “one of the best policemen I have ever worked with.”

The fact that his immediate supervisor never scolded Perez or ordered him back to work indicated retaliation, the commission found.

Perez’s federal lawsuit, filed in 2012, alleges that the city failed to properly pay officers for overtime beginning in 2009. U.S. District Judge Carl Barbier last month barred officers from seeking any overtime pay under the lawsuit before April 2011, saying Perez failed to act quickly enough.

Just how much the lawsuit could cost the city is uncertain; it may depend on how many officers come forward to claim unpaid overtime.

Perez’s attorney, Eric Hessler, said the Civil Service Commission ruling could impact damages awarded in the federal lawsuit if Perez prevails on behalf of the class of cops who claim they worked for free.

“When you look at the timing, the facts, his record, there was only one thing that made sense. That was retaliation,” Hessler said.

Perez launched a private security firm last year that was hired by three Bourbon Street strip clubs to bolster their protection amid a manpower shortfall in the NOPD.

Follow John Simerman on Twitter, @johnsimerman.