The shrill wails of sirens resounded throughout Ukraine's eastern rust belt on May 20, a rallying call for miners and steelworkers to unite against separatists seeking to take over their region.
Industrial workers have remained largely on the sidelines of the smoldering conflict in eastern Ukraine, where pro-Russian militants have been occupying key government buildings in a dozen cities.
But with separatists increasingly disrupting business, industrial bosses and trade unions are urging workers to rise against the insurgency.
Coal and steel magnate Rinat Akhmetov, who has an estimated 300,000 employees on his payroll, this week called on his employees to stage peaceful protests at their workplaces.
"The rally will start tomorrow at noon with a siren ringing at all industrial businesses of the Donbass in support of peace and against bloodshed," he said in a televised address late on May 19, adding that sirens would ring daily at noon "until peace is established."
In his sharpest condemnation of the separatists so far, Akhmetov said people were "tired of living in fear and terror" and warned that the violent tactics used by separatists would spell disaster for the economy and lead to "genocide" of eastern Ukraine.
"I am calling on everyone to unite in our fight," he wrote. "For Donbass without weapons! for Donbass without masks!"
Akhmetov, Ukraine's richest man with a fortune estimated at more than $11 billion, wields huge clout in the region and his calls are likely to be heeded.
Last week, Akhmetov's Metinvest company, one of the most powerful in the region, dispatched miners and metalworkers to the city of Mariupol to restore order after bloody clashes between Ukrainian troops and rebels.
The workers helped dislodge pro-Russian insurgents from the city hall and clear away barricades surrounding the building.
They now patrol the city alongside police.
Far from all Donbass miners pledge blind allegiance to Akhmetov. Many say they feel a world apart from Kyiv and its pro-European protests that triggered the political crisis in Ukraine last fall.
There's lingering distrust for Kyiv authorities old and new, as well as resentment for what many here perceive as ingratitude toward Ukraine's breadwinning east.
But the coal and mining industry employs about half a million people in eastern Ukraine.
Just weeks after Russia's annexation of Crimea, the prospect of losing their livelihoods if separatists were to succeed in bringing the region into Moscow's fold is spurring industrial workers to rally against the insurgents.
"The vast majority of miners are against separatists," claims Mikhailo Volynets, who heads Ukraine's Confederation of Independent Trade Unions (KVPU). "They understand that they will lose their jobs."
The KVPU, along with five other trade unions, issued a statement on May 19 urging all workers across eastern Ukraine to join forces against the rebels.
They firmly condemned militants' attempt to block all railway deliveries in and out of the Donetsk region, with the exception of goods bound for Russia.
"This outrageous fact confirms that separatists are forgetting themselves," the statement said. "Such actions will definitely lead to the worsening of the living conditions of people in eastern parts of Ukraine and an economic collapse of the entire country."
Mikola Volynko, the head of the Trade Union of Donbass Miners, is not among the signatories.
But he couldn't agree more.
For weeks, he has relentlessly predicted his region's economic ruin should the separatists have their way.
"Federalizing the region or joining Russia will kill the mines and will leave Ukrainian miners without work," he warns.
Russia's own coalmining industry has seen a sharp decline since Soviet times.
Coal currently accounts for under 15 percent of Russia's energy consumption.
According to Georgy Krasnyansky, chairman of the Russian Organizing Committee of the World Mining Congress, the share of coal in Russia's energy consumption has dropped almost fourfold over the past 50 years.
Flush with oil and gas, Moscow would unlikely keep eastern Ukrainian mines running.
"There are enough unemployed Russian miners as it is," notes Volynko.
Fellow trade unionist Volynets believes miners are poised to play an instrumental role in the Ukrainian crisis.
Whether they will succeed in turning the tide against separatists, however, is another question.
"Many people in the east now carry weapons," says Ukrainian political analyst Ihor Burakovskiy. "You can't really expect miners and steelworkers to go and storm separatist checkpoints. If we were talking about rallies, then miners could easily overwhelm separatists by their numbers. But the situation is completely different."
RFE/RL Russian Service correspondent Dmitry Volchek and RFE/RL's Ukrainian Service contributed to this report.
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