The rail union is planning to switch off Opal card readers as part of its ongoing industrial dispute with the NSW government over pay and conditions. 

The date for the shutdown has not been determined and the government has yet to be notified.

Last month, the Rail, Tram and Bus Union (RTBU) intended to switch off the readers to give commuters free travel, but cancelled its plan at the last minute because of legal threats from the government.

The Transport Minister David Elliott announced that the government had received legal advice that it could be "illegal" and lodged an application in the Fair Work Commission to stop the Opal action.

The union subsequently made the decision to abandon its plan before the hearing. 

Now, a month later, the RBTU has held a ballot and 97 per cent of members who voted, supported reviving the action to switch off the readers.

"This has sent a very strong message to the NSW government that RTBU members are prepared to fight for their right to take action and the EA they deserve," a letter to union members authorised by union secretary Alex Claassens said. 

The relationship between the union and the government has become increasingly hostile which led to Premier Dominic Perrottet threatening to terminate the enterprise agreement last month.

The union has been conducting rolling industrial action which has caused significant delays and disruptions on the Sydney train network for commuters, at times this year.

Union members will meet to decide when this new round of action will go ahead. 

Mr Elliott this afternoon called on the union to reconsider its plan.

"Again we see the unions threatening economic vandalism against the taxpayers of NSW," he said.

"The Opal card readers are taxpayer assets and the unions interfering with wiring and switches to turn them off is both unsafe and ridiculous."