About 4,000 workers at a northern Greek gold mine and their supporters are demonstrating in Athens, in the most significant labor challenge the new radical left-led government has faced since its election in January.

Protesters fear job losses because the governing Syriza party has fought the privately-owned mine on environmental and financial grounds. Authorities have temporarily revoked a permit for a key ore enrichment plant at the Skouries mine, and accuse the mining company of encouraging the protests.

Police closed major roads as miners marched to the Development Ministry Thursday, where they shouted slogans and banged their hard hats on the ground. The protesters were later planning to march to Parliament, while a counter-protest by leftists and anarchists who oppose the gold mine was planned for later in the day.