At this stage there is no planned announcement of job cuts but they did take place in 2015 when Glencore made a similar move.

Glencore operates 11 mines that export through Newcastle and six in Queensland.

The Hunter and nearby mines are the Bulga, Glendell, Liddell, Mangoola, Mount Owen, Ravensworth and United Wambo open-cuts, the Integra and two Ulan underground mines and the Hunter Valley Operations open-cut, a joint venture with Yancoal holding 51 per cent.

Glencore has blamed the situation on the global economic impacts of COVID-19 suppressing demand for Australian export coal.

READ MORE: The Herald's Opinion, Glencore's short-term market fix

The temporary shutdowns follow the release of Glencore's half-year financial results on Thursday, which put the company billions of dollars in the red on lower commodity prices, higher costs and substantial write-downs of business value.

Although Glencore sells its best quality coal into the higher priced coking coal market for steel making, about 90 per cent of its product is sold as thermal coal for use in power stations in Australia but mainly in China, Japan and other Asian countries.

The company's public statement on the shutdowns ran to just eight sentences, but workers at each site were called in and briefed, and given a longer version of the same statement, setting out the duration and nature of their workplace closures.

Workers have been told they will be required to take leave during the shutdowns.

Glencore's response to the price squeeze has been endorsed by the main mining union, the CFMEU.

The northern district president of the CFMEU's mining and energy division, Peter Jordan, said he had met with Glencore yesterday morning to discuss the planned shutdowns.

"Further discussions at a site level are taking place with district union officials," Mr Jordan said.

"Two-week shutdowns will affect operations considered non-essential.

"They will be timed to coincide with school holidays, with workers able to use leave entitlements during the shutdown period.

"The union supports this approach as a way to protect permanent and contractor jobs at a time of economic volatility affecting global demand for coal."

Although the union described the shut-downs as affecting "non-essential" operations, Glencore and workers who spoke with the Newcastle Herald made it clear the aim was to stop mining as a start to reducing production.

It is understood, however, that skeleton crews will remain at work to load trains to send coal to Newcastle to meet existing contract obligations.

On Thursday, Glencore's chief executive Ivan Glasenberg briefed analysts and the media after the company's half-year results and said the coal market was oversupplied.

As it had made clear earlier in the week with its half-year production report (separate to the half-year financial report), Glencore plans to cut its coal production by about 14 million tonnes this year, bringing its forecast tonnage down from 132 million tonnes to 119 tonnes for the 2020 calendar year.

Glencore also mines coal in South America and South Africa but the bulk of the 14 million tonne reduction is expected to come from Australia.

To put those figures in perspective, Newcastle coal exports have totalled about 160 million tonnes a year in recent years, and Glencore's NSW production in 2018 was more than 55 million tonnes.

Although Glencore is the minority 49 per cent shareholder at Hunter Valley Operations, a Yancoal spokesperson confirmed the shutdowns affected it as well.

The shutdowns would include a combination of "temporary production and equipment shutdowns" coinciding with the holidays.

"HVO's focus is on taking necessary steps to continue operations, manage the current market volatility and limit the impact on our workforce," the Yancoal spokesperson said.

School holidays start on Monday, September 28, and school resumes on Monday, October 12, and the shutdowns are understood to start on the weekend after school finishes and conclude on the Sunday before pupils return.

Workers said the production profile at each mine site was different, therefore some sites would "park up" equipment and some may not need to take any action at all.

At least some workers were told that if prices had not risen by the end of the year, another shutdown would take place during the Christmas holidays.

In his briefing on Thursday, Mr Glasenberg told his audience that global demand for thermal coal had fallen by about 120 million tonnes.

"Yes, look, the coal market has been hit this year because of COVID," Mr Glasenberg said.

"It affected the demand in part of the major importing countries.

"India, for example, which normally imports around about 180 million tonnes of coal, we believe, is reducing the imports around about 35 million tonnes.

"You have China will be reducing imports around about 33 million tonnes.

"So we think the demand has been cut by COVID in the 985 million tonne seaborne market by about 133 million tonnes.

However, with that, the coal price has come down, so certain countries have cut production.

"We believe Indonesia could be down around about 50 million tonnes. So we believe, in our calculations, the markets lost supply of about 120 million tonnes.

"So demand has reduced more than the supply reductions, and therefore, we're getting a bit of this excess supply. It could correct itself with the lower prices. You will have further shutdowns around the world.

"No doubt, Indonesia, who are cash negative today, will reduce some of their production.

"We've reacted, like we always do, when you have falling commodity prices and oversupply in the market.

"And as you've seen, we put Prodeco [a Columbian open-cut] onto care and maintenance, and we've cut 7 million tonnes out of Australia.

"And hopefully, we believe with these actions by ourselves and Indonesia, the market will be back and re-balance, and you will have an upward movement on the pricing."

Glencore's half-year accounts repeatedly mentioned prices of $US60 a tonne but prices have fallen further than that.

In its statement to the media, Glencore said it needed to "align production levels with market demand, while providing the flexibility to ramp back up as economies recover from the effects of COVID-19".

"The changes are consistent with measures we have put in place in the past in response to challenging global market conditions," Glencore said in a reference to its 2015 production cuts.

Mr Glasenberg said long-term coal was "still a good business for us".

"It is a cash generator, not as high as it has been in the past with the falling coal prices," Mr Glasenberg said.

"However, even at these lower prices, it still generates cash for the company."

He said coal earned "about $US1.3 billion, $US1.4 billion EBITDA [earnings before income tax and depreciation] at current prices".

"So it's still a good EBITDA generator and a cash flow generator for the business. We'll continue assessing it, but coal should remain within Glencore right now."

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