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A three-day strike by Tube staff threatens travel mayhem for fans heading to the FA Cup Final at Wembley.

Nearly 80,000 fans will attend the Manchester City v Watford match on Saturday May 18, with thousands more travelling to FA Vase and FA Trophy Finals played back-to-back the next day.

It will be one of the busiest weekends of the year at the stadium, with many supporters using the Metropolitan and Jubilee lines.

But the RMT union today ordered 1,200 key maintenance and engineering staff to begin a three day strike starting on Friday 17 May in a safety row.

The union has accused Tube management of “hacking back” on vital train preparation and inspection schedules.

Peter McNaught, director of asset operations for London Underground, said: “We have plans in place to ensure we can deliver a Tube service for our customers.

"The safety of customers and staff is our top priority and our proposals do not compromise this.

"Train checks will continue daily, with every train thoroughly checked to guarantee safety. Our proposals are to change the frequencies of some less safety critical checks, with the regulator, the Office of Rail and Road, satisfied with our approach.

"We have actively consulted with the Trade Unions over this issue and we remain open for discussions on how to resolve this dispute without unnecessary industrial action."

A TfL spokesperson added: "Train preparation checks will continue daily, with every train still thoroughly checked in order to guarantee its safety. Our proposals are to change the frequencies of some less safety critical checks, with the Office of Rail and Road satisfied with our approach."

Staff involved in the industrial action are based at the Tube fleet maintenance depots across the Greater London area.

They are critical to the day to day operation of the Tube, used by more than four million people a day.

The three days of strikes would have an cumulative effect because safety inspections might not be carried out or repairs left undone, stopping some trains from entering service.

Trains must be inspected before they are allowed to enter service.

RMT members voted nine to one in favour of industrial action and the union refused to rule out further walkouts.

RMT union leader Mich Cash aclaimed the changes to train preparation and inspection schedules would have a “devastating impact on both service reliability and public safety.”

He said London Underground proposals would “decimate inspection procedures beyond all recognition.”

Mr Cash said: “The nine to one ballot result showed how angry Tube staff are at proposals LU is attempting to bulldoze through that would decimate the inspection and safety culture on the fleet.

“Despite that result Tube bosses have ignored the workforce and are pressing ahead and it is that intransigence that has left us no option but to confirm industrial action today.”

He called on LU to “pull back immediately rather than crash on regardless of the consequences of their actions.”

The union also ordered further industrial action including a work-to-rule across a number of areas including risk assessment.

It is demanding a halt to all the changes pending a “full safety examination of all safety aspects” takes place.

The dispute is separate from major rows over pay and job losses with further announcements of more strike ballots expected any day.

The Standard revealed last month Tube commuters face a Summer of Discontent with all the main unions joining in the pay battle.

Non-League Finals Day is staged at Wembley on Sunday May 19, Chertsey Town facing Cray Valley in the FA Vase before Leyton Orient and FC Fylde play in the FA Trophy.