Federal Greens senator Jordon Steele-John has accused Attorney-General Christian Porter of making "highly offensive" comments about a possible royal commission into mistreatment of people with disabilities.

Mr Porter said such an inquiry would be backwards looking, noting the government had spent $200 million to set up a national protective agency for disability care, despite the coalition agreeing to support a non-binding motion on Monday calling for a commission.

"This was a highly offensive comment from the attorney-general. Let's be clear, the hundreds of millions of dollars that the attorney-general was referring is for a watchdog that is all bark and no bite," Senator Steele-John told the ABC on Monday.

0:00 Senator Jordon Steele-John pushes for a royal commission into systemic abuse of people with disabilities 00:00 / 00:00 Share Share on Twitter

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Senator Steele-John, who uses a wheelchair and is a vocal advocate for disability rights, wants the inquiry to examine the systemic abuse and mistreatment of people in workplaces, residences and educational settings.

Prime Minister Scott Morrison has indicated his government will on Monday support a motion calling for a royal commission into the treatment of people with disabilities.

However, the details and timing of such an inquiry have not yet been established.

Attorney-General Christian Porter said the royal commission would likely look into state-run facilities, and therefore need approval from state and territory governments.

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"You would need assurances from the states, and I think, likely letters patent from the states, before you get to that point," he told the ABC's Insiders program on Sunday.

"I think it's a matter that needs to be discussed very closely with the states."

The prime minister said the federal government would develop the royal commission's terms of reference in consultation with the states and advocates in the disability sector.

He said the royal commission needed clear and specific parameters.

"Otherwise it is just a general conversation which runs the risk of not landing it any quite targeted recommendations that you can act on," he told reporters in Tasmania on Sunday.

"We want to make sure that anything further we do in this area is done with that well-considered terms of reference and directions to ensure that it can do its job."

The motion calling for a royal commission is backed by Labor, the Greens and crossbench.

The prime minister used stalling tactics to block a vote on the issue last week, but later indicated he supported the idea.

The Greens have been calling for a royal commission into the disability sector since 2015.

Senator Steele-John believes the slow progress towards an inquiry points to a key issue at play.

"The root cause of this is the devaluing of our lives as disabled people," he said on Sky News on Sunday.

"We are seen in this country as less-than-human by the majority of society."