Glennies Creek coal mine.
As many as 500 people could lose their jobs as work at two coal mines is suspended in NSW's upper Hunter Valley, a union says.
Workers at Glennies Creek underground and Camberwell open cut mines, near Singleton, were warned about the looming cuts on Friday, with a final decision set to be announced this coming week.
The mines are owned by Integra, a subsidiary of Brazilian mining giant Vale, and have been a major source of local employment for years.
Peter Jordan of the Construction Forestry Mining and Energy Union (CFMEU) said workers were told that the mines will be put under care and maintenance - essentially suspending them for the foreseeable future.
Staff at Glennies Creek were ordered to stop work immediately until next Friday, when a full announcement on their future is expected.
Miners at Camberwell continued working but were put on notice that their jobs are under threat.
The CFMEU is meeting with Integra on Wednesday.
"The workers are all in shock at the moment and the anger is starting to set in, there's no doubt about that," CFMEU district secretary Peter Jordan told AAP.
"Integra's telling the employees that it's due to lower coal prices and the high Australian dollar.
"We've got 350 members engaged at both the mines and when you add support staff to that you're talking about 500 Integra jobs."
AAP has contacted Integra for comment.