A spokesman for the company said this was a considered management decision given the current oversupply situation and reduces the need to push incremental sales into an already weak pricing environment.

We remain confident in demand growth for our products and believe that the supply and demand balance will be restored in the medium term, he said.

The shut downs will result in reduced output of about 5Mt from the Australian assets.

A spokesperson for BHP Billiton's Mt Arthur mine said they were not planning similar action. 

Thousands of mineworkers have been caught short by mining giant Glencore’s announcement of a three-week Christmas shutdown, the Miners’ Union said today.

CFMEU National President Tony Maher said the company did not consult with workers and the compulsory standdown may breach workplace agreements.

“Glencore’s decision to spring this on workers with only a month’s notice will catch some workers short of annual leave and force them to change holiday plans,” said Mr Maher.

“Growing casualisation in the industry means the shutdown will be a disaster for labour hire workers who will simply be told they’re not needed over Christmas.

“It demonstrates the arrogance of management, who could have negotiated with workers to find mutually suitable ways to reduce production – like letting workers take public holidays.”

The shutdown comes as other mine operators move to force workers into working on Christmas and Boxing Day, showing increasing disregard by employers for the industry’s workers and their families.

However Glencore’s move to take some supply out of the market is welcome, with short-sighted overproduction of coal driving a cycle of lower prices and cost-cutting, said Mr Maher.

“Glencore’s reduction in production will most likely be met by increases by other mine operators.

“We urge all coal mining companies to consider ways to look at ways they can reduce production and tackle the oversupply damaging the industry.”