Action's remaining 33 Renault diesel buses were supposed to be retired at the end of 2022 and replaced with 12 electric buses and 26 low-emission diesel buses.

But the government says supply chain issues have delayed their delivery.

A government spokesman said the older buses are only being used as a backup in cases such as when a more modern bus has broken down. He said the buses will be "progressively phased" into the fleet over the first half of this year.

Opposition transport spokesman Mark Parton said the government should have been transparent about the continued use of the orange buses.

"We understand there have been supply issues and everything else but I think they should have come clean with people on this," he said.

"The reality is there is a bunch of people with disabilities that mean it's not possible for them to get on these buses."

Mr Parton said that while the buses may only be used occasionally, it wasn't good enough.

"I think it's like being pulled over by police and saying 'Well I only speed 5 per cent of the time'. It just doesn't cut it. They've had a decade to sort this out and they failed again," he said.

There are 456 buses in Transport Canberra's fleet and the Renault buses only account for 33 of those.

The national disability standards for accessible public transport were implemented in 2002 and had target dates for when public transport had to meet certain standards.

Under the standards, the old orange Action buses were supposed to be retired by December 31, 2022.

Transport Minister Chris Steel is on leave. An ACT government spokesman said the government was working with the ACT Human Rights Commission to ensure it was aware of the impacts.

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But the spokesman said the buses would only be used in exceptional circumstances.

"In the interim, while the new buses are still being delivered, Transport Canberra will manage the allocation of buses to minimise the use of the Renaults as backups only," he said.

"This will mean they are primarily used to cover unplanned issues such as breakdowns or late running to maintain reliability for our customers."

The spokesman said people could use Transport Canberra's journey planner to see whether their bus was compliant with the standards.

The government would work with customers to ensure specific buses are allocated to services where compliance with the standards was critical for particular users.

The government came under fire last month after the release of the 2023 timetable showed significant cuts to suburban services. The government published the timetable with no public notification.

These cuts have been attributed to light rail roadworks and not the delayed delivery of the buses.

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