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London Underground users are set to be hit by fresh strike action before the launch of the Night Tube.

RMT union members have voted to back a walkout of maintenance and engineering staff in a row over pay and working conditions.

The union claims Transport for London has refused to discuss outstanding pensions issues until after the launch of the 24-hour service in August.

A union spokesman could not confirm when the strikes would take place and said the result would be considered by RMT's executive.

RMT general secretary Mick Cash said: “RMT members have now shown their anger at the way that Tube Lines have attempted to tie in attacks on pensions with the offer on pay and Night Tube.

There are also major unresolved issues over the Tube Lines staffing arrangements for the Night Tube and over Performance Related Pay.

“The ballot result will be considered by RMT’s executive and now that the members have shown their anger it is absolutely essential that there is the earliest possible resumption of serious and meaningful talks on these issues and the union is ready to engage in those talks.”

Mayor of London Sadiq Khan announced that Night Tube services would begin on August 19 on the Central and Victoria Lines.

Night services on the Jubilee, Northern and Piccadilly lines will follow in two separate phases later in the autumn as new Tube drivers complete their training and final preparations are made.

Around 200 part-time drivers are currently taking part in a 14-week training programme for the new service.

The engineers' strike ballot result is the first faced by the new mayor since he took over from Boris Johnson earlier this month.

A TfL spokesman confirmed the strike would not affect the Central or Victoria Lines.

London Underground chief operating officer Steve Griffiths said: "We have made the same fair and sustainable four-year pay offer for Tube Lines maintenance staff as has been made for staff employed by London Underground.

"Pension arrangements for Tube Lines maintenance staff have been the subject of separate ongoing discussions, and we agree that it's important that these talks resume as soon as possible so the dispute can be resolved."