SEIU 509, a health care and human services union that represents 20,000 workers in Massachusetts, is supporting state Rep. Liz Miranda in her bid for the Second Suffolk Senate seat.

“Liz has been a proven leader on the issues affecting our membership and the people they serve,” Peter MacKinnon, the union’s president, said in a statement. “From her advocacy on Black maternal health to safeguarding access to abortion, Liz ensures the most urgent priorities in our communities are brought to light. She is a true example of government for all.”

Miranda is up against fellow state Rep. Nika Elugardo, pastor Miniard Culpepper and former state Sen. Dianne Wilkerson for the Senate seat, which opened up with the planned departure of state Sen. Sonia Chang-Diaz. The Democratic primary is set for Tuesday, Sept. 6.

State Rep. Liz Malia, a House colleague who is retiring this year and represents Jamaica Plain, also said she’s backing Miranda for the Senate post, calling her a “coalition builder” with a “big heart.”

Miranda has also picked up support from the Environmental League of Massachusetts Action Fund, the Mass. Nurses Association and City Councillors Ruthzee Louijeune and Tania Fernandes Anderson.

The Second Suffolk Senate seat covers Dorchester, Mattapan, Roxbury, Jamaica Plain and Mission Hill.