The White House confirmed the development in a statement:
Over her long career in public service - as an advocate for environmental justice in California, state legislator, member of Congress and Secretary of Labor - Hilda Solis has been a tireless champion for working families. Over the last four years, Secretary Solis has been a critical member of my economic team as we have worked to recover from the worst economic downturn since the Great Depression and strengthen the economy for the middle class. Her efforts have helped train workers for the jobs of the future, protect workers' health and safety and put millions of Americans back to work. I am grateful to Secretary Solis for her steadfast commitment and service not only to the Administration, but on behalf of the American people. I wish her all the best in her future endeavors.
More from the AP:
In a message to colleagues, Solis said she made the decision to leave after discussing it with her family and close friends.
One of the highest-ranking Hispanics in Obama's administration, Solis has won praise from labor unions for aggressive enforcement of wage and hour laws and job safety regulations. But business groups have criticized her as not taking a more cooperative approach.
"Leaving the department is one of the most difficult decisions I have ever made, because I have taken our mission to heart," Solis said. "As the daughter of parents who worked in factories, paid their union dues and achieved their goal of a middle-class life, and as the first Latina to head a major federal agency, it has been an incredible honor to serve."
President Barack Obama called Solis "a tireless champion for working families."
"Over the last four years, Secretary Solis has been a critical member of my economic team as we have worked to recover from the worst economic downturn since the Great Depression and strengthen the economy for the middle class," Obama said in a statement.
Solis said she is proud that 1.7 million people have completed federally funded job training programs under her tenure. Her agency oversaw the spending of about $67 billion for unemployment insurance benefits, job training and other job placement and worker protection programs under Obama's economic stimulus package.
Separately, the White House said Wednesday that Attorney General Eric Holder, Health and Human Services Secretary Kathleen Sebelius and Veterans Affairs Secretary Eric Shinseki would remain in their posts.
Holder and Sebelius have been frequent targets of Republican foes in Congress. The attorney general has been criticized for the government's handling of Operation Fast and Furious, a gun-running investigation gone awry. Sebelius is in charge of putting in place Obama's health care overhaul law, which Republicans have failed to repeal.
This story is developing. Check back for more updates...