City agencies are spending big money prettying up official vehicles at a car wash empire that is currently being investigated for alleged dirty labor practices, the Daily News has learned.

The city has paid Lage Management Corp. more than $170,000 for car cleanings since 2010, including $12,207 in the last three months, says Public Advocate Bill de Blasio, who wants the business relationship to stop.

“It’s better to have a dirty car than a dirty conscience,” argued de Blasio, who has written to Mayor Bloomberg to demand an immediate end to city use of dozens of Lage car washes in the five boroughs.

In recent weeks, Lage owner John Lage found himself in legal trouble yet again when state Attorney General Eric Schneiderman opened an investigation into allegations that Lage workers are being cheated out of wages.

In 2009, Lage paid out $3.4 million in back pay and damages to workers after the federal Labor Department filed suit.

“New York City tax dollars should not enrich a bad actor that openly violates the law and exploits working people,” de Blasio charged in his letter to Bloomberg.

Marc La Vorgna, a spokesman for the mayor, said the issue de Blasio raised in his letter is being evaluated.

De Blasio is backing an effort by advocacy groups, including New York Communities for Change and Make the Road New York, to end alleged labor abuses in the local car wash industry.

Amid an ongoing push by the Retail, Wholesale and Department Store Union to organize Lage employees, scores have come forward to complain they are making just $5.50 an hour — or $1.75 below state minimum wage. They also complain of being denied overtime, having their tips grabbed up and being subjected to harsh working conditions.

“None of this is true,” said Lage’s son and business associate Michael Lage, who called the accusations a “smear campaign” to support the unionization drive. He singled out Make the Road New York for blame.

“This group’s thinly veiled agenda is to siphon off a portion of our employees’ hard-earned pay through compulsory union dues,” Lage said in a statement to The News.

Lage “is very proud of the fact that we have created hundreds of jobs that people rely on to support their families, and we believe we have had a positive impact on these communities.”

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