The National Bus and Rail Union is warning that unofficial 'wildcat' strikes by Bus Éireann workers could happen again.

The NBRU has insisted they were not involved in yesterday morning's action, which shut down virtually all Irish Rail and Dublin Bus services for several hours.

The union also says that, despite reports, they have not received notice of legal action from those companies looking to recoup lost profits.

Official union action, meanwhile, is now into its ninth day, with workers taking part in an all-out strike over proposed cost-cutting measures at the embattled transport company.

There have been renewed calls for Transport Minister Shane Ross to get involved and facilitate talks between Bus Éireann management and the unions.

Yesterday, Minister Ross again insisted that he would not intervene - saying the Workplace Relations Commission and Labour Court exist to deal with such disputes.

General Secretary of the NBRU Dermot O'Leary says until a resolution is reached, he cannot guarantee there won't be more wildcat strikes.

He explained: "My union was not involved, I had no knowledge of it.

"I've been explaining to people for weeks and weeks that this issue at Bus Éireann could possibly develop into something people like me could not control. So if it happened once, than obviously people could deduce that could happen a second time."

He added: "I would repeat to people at Bus Éireann to remain in dispute with their employer until such a time that that dispute is resolved."