Prime Minister Scott Morrison has written to the states and territories asking for their support in establishing a joint inquiry into abuse in the disabled sector.

New South Wales, Victoria and South Australia have confirmed they are behind the probe, but a formal announcement is not expected until Mr Morrison hears back from the other leaders.

Federal Cabinet discussed establishing a royal commission on Tuesday night.

In his letter, Mr Morrison called on all governments to work together.

"I am now seeking your in-principle agreement for the establishment of a joint royal commission and the most appropriate consultation pathways to progress this important matter," he wrote.

The Prime Minister does not need the approval of the states and territories to call a royal commission, but has warned the scope would be limited without it, given services like health, mental health, education and justice can be regulated by the state.

Mr Morrison also asked leaders to sign up to a cost-sharing arrangement.

"I think we can all agree that violence, abuse and neglect of people with disability is abhorrent and that we should be doing all we can to ensure a safe and secure Australia," Mr Morrison wrote.

The step comes after the Prime Minister backed a motion supporting the inquiry in Federal Parliament in early February, under pressure from Labor and the Greens.

The Coalition came under significant criticism at the time, amid allegations they only supported the motion because they were afraid of losing another vote on the floor of Parliament.

Opposition Leader Bill Shorten also wrote to the states and territories, asking for their backing for the royal commission.

'We're looking forward to working with the Government'

Disability advocate and Greens senator Jordon Steele-John said the Prime Minister needed to do more than just write letters.

"We are winning but we have not yet won. This has been a very long process," he said.

"For five years disabled people have been calling for a royal commission into this issue."

According to National Disability Services, people with a disability are 1.5 times more likely to experience abuse, neglect, violence and exploitation than people without a disability.

"We support a royal commission because we understand that people with disability, like everyone else in our community, have the right to live free of the fear of abuse or neglect," chief executive officer David Moody said.

Mr Morrison has repeatedly said he was never opposed to an inquiry, but this is the first time he has expressly supported the matter.

Shadow Social Services Minister Linda Burney said the Prime Minister was shamed into agreeing to the inquiry against his will and now wanted to shift the cost.

"It’s a cheapskate move to try and offload the cost of this royal commission to the states," she said.

The Disabled People's Organisations Australia said a probe into the sector was well overdue.

"We're looking forward to working with the Federal Government to make the terms of reference inclusive of all people with disability," Therese Sands from People with Disability Australia said.

The organisation implored the Federal Government to make sure people with a disability are provided with extra services like counselling or legal advice so they can properly participate in the process.

The Coalition Government has called five royal commissions during its past two terms in office, including inquiries into the trade union movement, Labor's home insulation program, youth detention in the Northern Territory, banking misconduct and aged care.

This would be the sixth royal commission in as many years, with $100 million pledged for the aged care royal commission process and an estimated $75 million spent on the banking royal commission.