The Federal Court in Melbourne has started hearing a case that could result in a big pay rise for 20,000 intellectually disabled workers.

Gordon Prior of Ararat in Victoria and Michael Nojin from Coffs Harbour in New South Wales are intellectually disabled men who say they have been discriminated against.

Their lawyers are arguing their wages were driven down to unfair levels because of the method of assessment used to calculate their pay rates.

The men were paid as little as $1.79 an hour.

They say they could be earning more than $10 an hour if a different assessment tool was used.

Under the current system, a worker's competency and productivity are measured by answering a series of 16 questions.

If they get one wrong, they fail the category and their wages are cut.

If successful, the case may overturn the Australian Disability Enterprises Scheme, which is designed to get more disabled people into work and has been operating for seven years.