The National Disability Insurance Scheme participant, whose name was suppressed by the Administrative Appeals Tribunal, asked the agency to review new plans that reduced her support compared to her first one.

Tribunal deputy president Gary Humphries last week blasted the NDIA, administering the massive social reform,  for decisions that were "slow and difficult to interpret" and found the problem was common for participants.

"It seems to the tribunal entirely inappropriate that a participant, working with finite resources and coping with the added burden of a disability, should need to be left in doubt as to the status of decisions made affecting his or her entitlement to the benefits conferred by the legislation, yet this is precisely the situation many applicants to the tribunal have found themselves in recently," he said.

In a decision whether to stay the new NDIS plan for the woman, Mr Humphries said the agency had not always been transparent in taking steps to review its plans for participants.

"The tribunal urges the responsible minister to consider as a matter of urgency the circumstances which give rise to this entirely unsatisfactory state of affairs, and to assess what measures, administrative or financial, might be required to mitigate it."

The woman had asked the tribunal to review the NDIA's decisions about her support, but Mr Humphries found he lacked jurisdiction to stay the new plan.

However the tribunal is yet to rule on whether the level of support provided under the new plan is appropriate.

Mr Tehan said he met with the NDIA to discuss the AAT findings and that the agency was making improvements.

An NDIA spokesman said it was focusing on early resolution of AAT concerns with participants, and had a team to address outstanding reviews and make improvements.

Changes to its services had also lowered the number of reviews and complaints in pilot locations, he said.

Canberra barrister representing the woman, Allan Anforth, said the agency's decisions were often vague and difficult to understand.

The appeal system under NDIS legislation was too slow and let the agency avoid the tribunal's scrutiny, he said.

"An appeal is rarely listed for hearing before the year is up and the plan under appeal is replaced by another," he said.

"The NDIA will then argue that there is no point in the tribunal hearing the appeal because the plan under appeal is now non-existent and the appeal is a waste of time.

"The system is broken. Corporate culture comes from the top and those at the top need to do something now."

The Turnbull government in October rejected a call to delay the full roll-out of the NDIS, despite a major report finding the current timetable was compromising the quality of care and threatened the scheme's financial viability.

The Productivity Commission found the current timetable simply "will not be met" as the scheme struggled under a "tsunami" of demand.

However it also said the NDIS was already improving the lives of many participants, their families and carers.