Democratic presidential frontrunner Hillary Clinton picked up another major endorsement on Tuesday when the Service Employees International Union announced it would back her campaign.

The group, which backed Barack Obama in 2008, includes about two million employees in the healthcare industry. The SEIU said in a press release that the endorsement comes after a “rigorous, months-long member engagement process.”

PHOTOS - On the Stump: Hillary Clinton's Presidential Campaign

The announcement is another setback for Bernie Sanders, whose supporters were working hard to lobby the union to endorse the Vermont senator.

“Hillary Clinton has proven she will fight, deliver and win for working families,” SEIU International President Mary Kay Henry said in the statement.

“As president, I will be proud to stand with SEIU and fight alongside them—to defend workers’ right to organize and unions’ right to bargain collectively, to raise incomes for working people and the middle class, and to ensure that hardworking Americans can retire with dignity and security,” Clinton said in a statement after the endorsement was announced.

Clinton picked up another major labor endorsement when the American Federation of State, County and Municipal Employees (AFSCME) endorsed her last month. The group, which also threw its support behind Clinton in 2007, says it's the nation’s largest and fastest growing public services employees union, with more than 1.6 million members.