Twenty-two Romanian workers on Thursday refused to leave an ancient mining gallery in a last-ditch bid to get MPs to vote a bill that would clear the way for a gold mine there.

"We are very worried about their situation," said Catalin Hossu, spokesman for Rosia Montana Gold Corporation (RMGC), a joint company in which Canada's Gabriel Resources holds an 80-percent stake.

The employees of RMGC descended into the Roman-era mine Wednesday after Romanian Prime Minister Victor Ponta said a draft law intended to speed up the project would probably be voted down by Parliament.

In a separate incident, archeologists opposing the mine have said they had to end restauration work at the site after being assaulted by RMGC employees.

Gabriel Resources plans to open Europe's largest open-cast gold mine in the Transylvanian village of Rosia Montana.

The company acquired a mining licence in 1999 but has been waiting ever since for a crucial permit from the environment ministry.

To speed up the opening of the mine, Romania's centre-left government last month submitted a bill that would make it easier for the company to expel villagers living near the site.

But the draft law sparked an outcry and thousands of protesters over the last 10 days have taken to the streets across the country every evening.

Gabriel Resources wants to extract 300 tonnes of gold using an average of 12,000 tonnes of cyanide a year.

It promises 900 jobs will be created during the 16-year extraction period, with added economic benefits for locals.

Scientists from the Romanian Academy and environmental rights groups such as Greenpeace say the mine will be an a ecological time bomb, while archeologists warn it threatens ancient Roman gold mines.

Gabriel Resources on Wednesday told AFP it may sue for $4 billion (3 billion euros) in damages if Romania's parliament blocks its project.

"If the draft legislation is rejected then the company will provide formal notification to Romania of its intentions to commence litigation for multiple breaches of international investment treaties... with a claim of up to $4 billion", Jonathan Henry, CEO of Gabriel Resources, wrote in a email.