The Chief-Leader, the city’s influential weekly newspaper for civil-service union members, berated Mayor Bill de Blasio for his ethical lapses and endorsed one of his challengers.

“Someone who ran for office championing progressive ideals has behaved more like a clubhouse politician more inclined to take care of big contributors than serve the voters,” the paper charged in a Thursday editorial.

The scolding came down as rogue fundraiser Jona Rechnitz took the stand in federal court to describe his pay-to-play relationship with City Hall.

Union voters were an essential part of de Blasio’s winning coalition in 2013, when the Chief-Leader gave him its full-throated support.

But this year, the paper gave its formal blessing to Reform Party candidate Sal Albanese.

The mayor was unconcerned.

“Teachers, sanitation workers and unions representing hundreds of thousands of working New Yorkers are backing his re-election campaign,” said campaign spokesman Dan Levitan.