The Obama administration will make the "strongest case possible" for controversial "card check" legislation, Labor Secretary Hilda Solis pledged Monday.

Solis told a crowd at the AFL-CIO's annual convention in Pittsburgh that she and President Obama would fight to bolster workers' rights, which she said were "under assault."

"Workers are under assault, and they need a voice on the job that unions will provide," Solis said. "And that's why I will work with the White House so that together we make the strongest case possible for the Employee Free Choice Act."

Solis sent a signal that the administration would vigorously support the Employee Free Choice Act (EFCA), a controversial piece of union organizing legislation which has seen its prospects wane since the opening months of the administration.

Solis rejected claims that the bill would increase costs for businesses, saying that laborers need a more pronounced voice in the workplace.

"It's not enough to just have fair wages and a safe workplace; workers also need to have a voice on the job. And some people say that, given the state of the economy, we can't afford unions right now," she said.

"Well, they got it backward: today unions are more important than ever," Solis added.

Watch the portion of Solis's speech in which she discusses the card check bill below: