Rail operator Southern is taking legal action in a bid to prevent three days of strike action going ahead this week.

Mick Cash, chairman of the Rail, Maritime and Transport union (RMT) asked the provider for talks with conciliatory service Acas today ahead of industrial action planned for later this week.

But he was rebuffed by Southern, after the operator said peace talks were “no longer an option” and that ploughing ahead with industrial action was “union militancy”.

RMT members are due to walk out between Tuesday, October 11 and Thursday, October 13, with an extra 11 strike days scheduled before the end of the year.

The two sides have been at loggerheads for months over the role of conductors.

In a statement on their website, Southern claims it is safe for drivers to close doors.

The RMT argues commuting the role of on platform conductors to on-board supervisors (OBS) would put passengers at risk.

Last Friday the union encouraged conductor members to accept the OBS role in order to prevent "mass sackings”.

RMT general secretary, Mick Cash today said: “RMT can confirm the receipt of a formal legal challenge from Southern Rail in the guards safety dispute.

“It is appalling that rather than sitting down with us at ACAS today to seek a resolution the company have chosen to run to the courts under the cloak of the anti-union laws.

“The union intends to continue with the planned action and is examining the details of the paperwork."

A Southern spokesperson confirmed: “We have written to the RMT about the validity of the dispute in light of recent developments.

"We await their response and  will consider all possible options to stop the strike and that includes a legal challenge."

RMT members have strike action planned between Tuesday, October 11 and Thursday, October 13.

Mr Cash added: "Despite the company spin today there is no climb down from the union. Our dispute remains on and the fight for safety continues despite the bullying and threats from Southern.

"We have a duty to issue our members with clear legal advice that protects their position in the teeth of the threat of mass sackings. That is what we have done."

A Southern spokesman responded: "We told RMT last week ACAS is no longer an option, having been there countless times without success.

“RMT had a chance last Thursday to shake hands on a deal with us and rejected it, only to then tell their members to accept the new role 24 hours later."

The spokesman added: “On Friday they told their conductor members to accept a deal, and then tomorrow they plan to strike against it. It is a situation which will leave our passengers baffled, and in that context we are presently considering all possible options to stop the strike.”

Charles Horton, CEO of Govia Thameslink Railway, Southern's parent company, said: "Now to go ahead with these strikes just days after telling conductors to accept our offer sets new standards in union militancy.

“They don't care that hundreds of thousands of commuters will face yet more travel misery this week. It's clear this is all about the union trying to hang on to power and control.”

RMT members have strike action planned between Tuesday, October 11 and Thursday, October 13.