The Retail, Wholesale and Department Store Union on Thursday announced its endorsement of Sen. Jeff Klein, the Bronx Democrat who is being challenged in a hotly contested primary.

“In the Senate, Jeff has been a staunch advocate for working families. He led the charge on Paid Family Leave, which gives employment security to so many working people when they are going through life’s most challenging moments,” said the union’s president, Stuart Appelbaum.

“Jeff has committed his legislative career to lifting up working families by making the essentials in life more affordable. From providing funding for childcare subsidies through the state’s Childcare Facilitated Enrollment Project to making free college tuition a reality for CUNY and SUNY students, Jeff’s leadership has enhanced the lives of thousands of our members in New York State. For these and so many more reasons the RWDSU stands with Jeff Klein on his re-election campaign and we look forward to continuing our work with him on legislation that helps working people across New York.”

Klein is the former leader of the now-defunct Independent Democratic Conference. In April, the IDC agreed to disband and rejoin the mainline Democratic conference fold in the state Senate amid a broader push to help the party gain majority control in the Senate chamber.

Under the agreement, Klein became the deputy minority leader serving under Sen. Andrea Stewart-Cousins.

Nevertheless, the unity agreement did not end the primary challenges some former IDC members face. This year, he is being challenged by Alessandra Biaggi.

Klein earlier this year was accused of sexual harassment by a former staffer. Klein has denied the allegation and it is being investigated by the Joint Commission on Public Ethics.