Queens lawmaker James Sanders put on free concerts, distributed flowers and gave seniors all-expenses-paid weekends in the Poconos — all with taxpayer dollars and the help of a local nonprofit whose mission was supposed to be senior housing.

Sanders, a former city councilman now serving as a state senator, steered nearly $1 million in taxpayer money to Margert Community Corp. over a six-year period. The Rockaways, Queens, group in turn spent thousands in pork-barrel cash boosting the popularity of its biggest benefactor.

The spending is now under investigation by US Attorney Preet Bharara’s office. At least two former Sanders staffers and two non-profit operators have been questioned by the FBI and three of them told The Post they were questioned about Margert.

The non-profit’s co-founder, Marion Moses, filed a complaint, under penalty of perjury, with Bharara’s office in January. They said the FBI visited them last week following the Post exposÉ.

“They asked about Margert,” co-founder Malisa Rivera said. “They were asking about the inner workings and . . . did we know someone who used to work for Margert.”

Sanders has denied the allegations by Moses and Rivera.

“I am confident that at all times I have conducted myself within the ethical and legal laws of this state and country. I am also confident that when the allegations against me are fully investigated, they will be determined frivolous,” he said Saturday.

Margert, which was founded in 1980 by two Catholic churches, is funded mostly with federal, state and city grants. The Rev. Fulgencio Gutierrez, pastor of St. Mary Star of the Sea and St. Gertrude parishes, chairs the Margert board.

He declined comment on the federal probe, but was astonished when asked about a $102,548 expense for travel in the 2014 fiscal year.

“We spent that much? Really?” he asked.

The Rev. James Cunningham, pastor of nearby St. Francis de Sales Church and the former chair of Margert’s board, said that “the priests were figureheads of Margert.”

“Father Fulgencio’s role is even less than mine was,” he said.

When Sanders put on his annual “Senior Extravaganza” at the lakefront Woodloch resort in the Poconos, Margert played a key role. Three busloads of guests enjoyed lavish meals, swimming in an indoor pool, horseback riding and sledding in the Pennsylvania countryside.

“Margert paid for the buses,” said Mike Duvalle, who worked for Sanders and attended the weekend retreats.