The American Federation of Teachers, the nation's third-largest labor group, has officially endorsed Hillary Clinton for president.

"For nearly a century, the American Federation of Teachers has worked to expand opportunity for the people and communities they serve. I'm honored to have the support of AFT's members and leaders, and proud to stand with them to unleash the potential of every American," the 2016 Democratic presidential nominee front runner said in a statement.

AFT's endorsement is the first international labor union endorsement of the 2016 cycle so far. The union includes 1.6 million members and retirees nationwide and is only smaller than the National Education Association and the Service Employees International Union.

"I know from my own family that teachers have the power to change lives. We need to make sure every child has access to a quality public education and teachers with the tools to help them succeed," Clinton said.

According to AFT President Randi Weingarten, "Hillary Clinton is the champion working families need in the White House."