The Australian Manufacturing Workers Union says it has called in Worksafe to investigate the contamination of nine workers with uranium at the Ranger mine.

The mine is surrounded by Kakada National Park and is one of the world's biggest suppliers of uranium.

The union says workers were asked to clean up a yellow cake spill three weeks ago when a vacuum machine could have been used instead.

The union's Northern Territory organiser, Steve Milne says some of the workers have tested positive for dangerous levels of uranium in their urine.

"Some of them are on the lower end," he said.

"One, I believe is about three times the acceptable standards of uranium exposure.

"Mind you, from our point of view, any form of exposure to uranium is a danger because uranium basically has some major consequences on a person's ongoing health," Mr Milne said.

But the mining company, Energy Resources of Australia (ERA), says the union is exaggerating concerns.

Business development manager, David Paterson says the workers' exposure to uranium was within safe levels.

"All of their exposure was well below any safe levels of exposure to radiation," Mr Paterson said.

"There is an annual dose level that is a safe level that is established for people that work at the mine and this was well below that level," he said.