Goodwill Industries, one of the nation's most successful and well-known charities, is paying its disabled workers way below the minimum wage because of a federal labor law that allows non-profit organizations to "pay disabled workers according to their abilities, with no bottom limit on the wage."

NBC News spoke with employees at Goodwill who feel that the pay is inadequate and degrading. "It's a question of civil rights," said Sheila Leighland, blind from birth, who quit her job at Goodwill store when her wage was cut to $2.75. "I feel like a second-class citizen. And I hate it."

Records received by NBC show that Goodwill has paid its disabled employees way below the minimum wage, with some receiving as low as 22 cents an hour.

"People are profiting from exploiting disabled workers," said Ari Ne'eman, president of the Autistic Self Advocacy Network. "It is clearly and unquestionably exploitation."

Exploitative as it may be, the practice of paying disabled workers less than minimum wage is legal. The U.S. Fair Labor Standards Act (FLSA) was passed in 1938. It sets the parameters for minimum wage, overtime pay, employer recordkeeping, and child labor, among other things. Workers with disabilities can be paid at "special minimum wages" if their employer receives a certificate from the Dept. of Labor Wage and Hour Division.

"Meaningful work deserves fair pay," Rep. Gregg Harper of Mississippi told NBC News. "This dated provision unjustly prohibits workers with disabilities from reaching their full potential." Harper hopes Congress will introduce a new bill, repealing the portion of the FLSA that allows special minimum wages.

But Goodwill Industries CEO Jim Gibbons sees things a little differently. He defended the wages, saying that Goodwill hires disabled employees in order to give them the fulfilling experience of having a job, not based on their abilities to work. The experience, he says, is more important than the wage.

"It's typically not about their livelihood. It's about their fulfillment. It's about being a part of something. And it's probably a small part of their overall program," he said.

Fran Davidson, whose son works at a Goodwill in Montana and makes $7.80 an hour, echoed Gibbons' sentiments. "I feel really good about it. I don't have to worry so much about him," she said. "I know he's not getting picked on, and he's in a safe place. He enjoys what he's doing, and he's happy, and that's what we like for our kids."

Today, Goodwill executives from the U.S. and Canada are set to meet in Grand Rapids, Mich. for a four-day Delegate Assembly conference. Kathy Crosby, CEO of Grand Rapids Goodwill, said she didn't expect the wage controversy to be on the agenda during the meeting. "We are really focused on meeting the needs of the future," said Crosby.