Bathrooms attached to the disused restaurant have long been left open, even overnight, for those at the nearby embassy encampment, as well as the public. But this week The Canberra Times found they were locked and the site surrounded by a metal fence.

ACT Greens leader Shane Rattenbury wrote to the National Capital Authority, which owns the land in the parliamentary triangle, this month demanding the facilities be restored.

In November, a group of activists from the embassy "evicted" the NCA from the hertiage-listed restaurant in an "act of sovereignty", before being removed by police days later.

Activists said authorities had since begun locking the toilet gates, slamming the move as a "serious breach" of human rights and a "major health risk" for the Ngunnawal Elders.

It is understood the fence has also been barring access to the toilets since the occupation ended on November 8.

Activist Albert Hartnett said those at the embassy were now surviving on bottled water and people were "starting to get sick down there" as the only drinking water was from groundwater taps in the park.

In a letter addressed to the NCA's chief executive Andrew Smith, Mr Rattenbury voiced further concern that general rubbish collection services in the area had also reportedly ceased since the Lobby Restaurant occupation.

"Continued denial of these services could regrettably by perceived as retribution for the recent incident," he wrote.

"The Aboriginal Tent Embassy has a long and proud history as a place of protest."

But in a written response to Mr Rattenbury on Friday, Mr Smith said there was still access to public toilets and shower facilities in the gardens of Old Parliament House near the tennis courts.

"Security contractors open and close these facilities on a daily basis for public use," he said.

A spokeswoman for the NCA said the authority had not stopped providing portable toilets to the tent embassy, but did not give any detail about the Lobby Restaurant bathrooms.

"The NCA has provided services of portable toilets to the Aboriginal Tent Embassy site for a number of years," she said.

Public rubbish bins throughout the Parliamentary Zone continued to be emptied weekly, the spokeswoman said.

Mr Hartnett said the bathrooms near the tennis courts were only open at certain times and members of the public had started using the embassy's portaloos since the Lobby restaurant toilets were closed.

Many members of the embassy now consider the situation to be "payback" for the November protest.

"I believe the NCA are flexing their political muscles because of it, at the risk of our elders," Mr Hartnett said.

"If this had occurred at an embassy of international standing, it would be condemned in every way."

It is understood the restaurant bathrooms were reopened briefly during a memorial service for renowned Indigenous activist Denis 'Bejam' Walker at the tent embassy a fortnight ago.

On Tuesday the place of protest, which officially began on Australia Day 1972, was unusually quiet. Two portable toilets remained beside a small pile of garbage.

In the coming weeks, the tent embassy hopes to raise money for portable showers.

While the Lobby Restaurant was renamed the 'Koori Rose Garden' cafe by activists during November's occupation, such signage has since been taken down, along with an Aboriginal flag.

The group had planned to turn the building into a cultural centre and cafe to support the tent embassy.

In November, documents obtained by The Canberra Times revealed the federal government was finalising plans to sell the empty Lobby restaurant in the weeks before the occupation.

One 63-year-old activist was arrested during the protest but has since been released on bail.

The Lobby Restaurant closed suddenly in December 2016 after a long-running stoush between its former owner and the NCA. Its prolonged vacancy has sparked renewed land rights tensions in the area.

With Katie Burgess