Energy Australia say some of their workers at Yallourn Power station are being harassed, with one employee claiming the word ‘scab’ was spray-painted on his fence.
The operator of the power station also claims other workers found stickers with the word ‘scab’ stuck to their cars, ABC reported.
However the CFMEU have rubbished the accusations.
The CFMEU and Energy Australia have been involved in an industrial dispute for over 12 months, with 75 workers locked out of the power station in June.
More than 30 CFMEU members have since set up camp outside the power station, but deny the protest was aimed at disrupting other employees working at the site.
The state vice-president of the CFMEU's mining and energy division, Graeme Middlemiss, says the union and its members had nothing to do with the harassment.
"None whatsoever," he said.
"We wouldn't condone action like that but we've yet to see proof that it actually occurred.”
Meanwhile, talks to resolve the dispute are ongoing.
CFMEU Mining and Energy Division District President Luke van der Meulen told Australian Mining the dispute centred around new enterprise agreements.
“It’s not about money,” he said.
“It’s about dispute clauses, rosters and operational structure.
“Energy Australia has reneged on a previous commitment to improve conditions.”