The Construction, Forestry, Mining and Energy Union says Xstrata intends to axe around 30 jobs from the Hunter Valley as part of wider job cuts at the company.
Yesterday Xstrata said rising costs had forced it to cut 600 jobs across its Australian coal operations as part of an ongoing business review.
According to the CFMEU Xstrata's Ravensworth and Ulan coal mines in NSW have been earmarked for layoffs, with around 15 frontline jobs to go at each operation.
The Daily Telegraph reports both mines have also been scaled back from seven-day-a-week operations to five.
ABC News reports CFMEU Northern District president Peter Jordan said the union had held talks with workers at Ravensworth.