Origin Energy says the coal stockpile at Eraring Power Station is at the upper end of its capacity despite a strike between Pacific National and its workers.
The company, which supplies coal to Eraring, locked out 120 workers responsible for scheduling, rostering and the safe running of the company's fleet of trains on Thursday after they opted to engage in industrial action.
An Origin Energy spokesman said it was monitoring the dispute.
Sources familiar with Eraring's coal stockpile suggested the levels were very healthy and contained enough coal to last for more than two weeks.
Rail, Tram and Bus Union (RTBU) director of organising Toby Warnes said the Sydney-based workers had been the "victims of Pacific Nation's attempt to drastically the axe wages and conditions" in recent years.
He said a section of the workforce stopped for 72 hours as negotiations broke down about wages and working conditions.
Pacific National then hit back by locking anyone taking part in the industrial action out of the workforce for a week from October 18.
"This is a deplorable move from Pacific National and a clear attempt to take advantage of a small section of the workforce whose wages and conditions have been slashed by tens of thousands of dollars over recent years," Mr Warnes said.
"But rather than treat its workers with the respect they deserve, Pacific National management has made the outrageous decision to lock these workers out of their offices."
Mr Warnes said Pacific National's move could have implications on freight operations if the dispute wasn't resolved soon.
He said they were "safety critical workers" that weren't "asking for much".
The union has been calling for fair pay, redundancy packages and better conditions, which they claim would be in line with similar jobs in comparable companies.
A Pacific National spokesperson slammed the "unnecessary and disproportionate" action the RTBU had taken, including 13 bans, and 288 back-to-back 15-minute stoppages.
"With this in mind, Pacific National has made the difficult but necessary decision to lock out any employees who engage in the stoppages," they said.
"We continue to bargain in good faith and encourage the RTBU to attend the next bargaining meeting with a spirit of compromise so we can reach a deal that delivers what matters for our people, shareholders and customers."
Pacific National said it had been bargaining with its planning team in NSW for an enterprise agreement for more than a year.
The spokesperson confirmed the lock out had not affected Pacific National services as the company put contingencies in place.
