President Barack Obama has appointed a key union activist as senior adviser to Labor Secretary Hilda Solis, another sign of the influence that organized labor wields in the Obama administration.

Mary Beth Maxwell spent the past five years as executive director of American Rights at Work, a nonprofit group pushing for passage of a bill to make it easier to form unions.

At the Labor Department, Maxwell will serve as a liaison to the White House Task Force on Middle Class Working Families, a group charged with raising the living standards of middle-class families by improving labor standards, boosting workplace safety and protecting retirement security.

Democratic leaders in Congress hope to bring some version of the Employee Free Choice Act to a vote this summer. Democrats are trying to rally enough votes to overcome an expected GOP filibuster.

Former Democratic Rep. David Bonior, chairman of the board at American Rights and Work, suggested Maxwell's new post would bolster union efforts to pass the labor reform legislation, also known as "card check."

"Her knowledge and experience will aid the administration and the Labor Department in supporting this and other policies to benefit working families throughout the country," Bonior said.

Business groups strongly oppose the card check bill, which would remove the right of employers to demand a secret ballot election before workers could form unions. J. Justin Wilson, managing director of the anti-union group Center for Union Facts said Maxwell's appointment shows "the outsized influence labor leaders hold over President Obama and the Department of Labor."

Solis also was a board member of American Rights at Work, a position she left after being confirmed to the president's cabinet.