ATHENS  - Hundreds of Eldorado Gold (ELD.TO) workers fearing job losses marched through Athens on Thursday, hours before a deadline imposed by the Canadian miner over permits expires.

Eldorado Gold last week threatened to halt new investment in Olympias, Skouries and the Stratoni mines from Sept. 22, unless the Greek government granted it permits and showed a willingness to engage in talks.

Workers in yellow vests and safety helmets gathered outside the energy ministry in Athens chanting "We won't back down!" They waved flags and held placards reading "YES to mines, NO to unemployment".

"We won't allow them to play with our future," a protesting worker told state TV.

Eldorado's investment in northern Greece, which employs about 2,000 people, is one of the biggest in the country since its debt crisis began in 2009. The miner spent nearly $2 billion in 2012 to purchase its Greek assets, including the Skouries mine along with Olympias and Stratoni projects.

The investment has long been viewed as a test of Greece's resolve to attract foreign capital.

Differences between Greece and the Canadian miner have dragged on for years, mainly over compliance with environmental regulations. Greece launched an arbitration process last week, saying it wanted to settle a long-running dispute over a metallurgical plant.

Since Eldorado's warning on Sept. 11, Athens has issued mine permits and detailed arbitration proceedings in an effort to defuse the tension.

The Vancouver-based miner has insisted that it will only reconsider its investment plans after receiving an outstanding permit for a Skouries flotation plant.

Eldorado's investment is a sensitive issue for Prime Minister Alexis Tsipras' party which strongly opposed the project before coming to power in 2015 but has also pledged to protect jobs.

A senior energy ministry official met with protesting workers on Thursday and told them the government intended to have discussions with Eldorado, a government official told Reuters, adding that the energy ministry remained focused on the arbitration process.

Separately, the chief executive of Eldorado's Greek business Hellas Gold told Skai TV on Thursday that an exchange of letters between Athens and the company this week increased hopes for a solution.

"Communication (between Greece and Eldorado) started at the beginning of the week ... we have exchanged letters and made efforts for a solution," Hellas Gold CEO Dimitris Dimitriadis told Skai television.

"Hopefully, these efforts will be fruitful".