Drivers on London Underground are to go on strike over the sacking of a colleague for failing an alcohol breath test.
The Rail, Maritime and Transport union said members will walk out from 21:30 GMT on 7 March to 03:59 on 8 March.
The union claims the type of breathalyzer used did not account for people with diabetes.
London Underground said the man was dismissed for failing two breath tests which were unaffected by the condition.
It said the case had gone through a full disciplinary hearing and appeals process, as well as a separate independent director's review.
'Misinformation and smears'
The transport authority said it had explored in detail the suggestion that diabetes could affect the breathalyser result, but concluded that the type of test it used was not affected by acetone, which is produced in the bloodstream of people with the condition.
Mick Cash, general secretary of the Rail, Maritime and Transport (RMT) union, said there had been a campaign of "misinformation and smears" against his organisation.
He said: "This action is the first stage as part of a rolling programme of industrial action and I urge all RMT London Underground train operators and instructor operators to stand firm together against this and any future injustices against RMT members."
Nick Brown, chief operating officer of London Underground (LU), said: "This indefensible strike is about one RMT member dismissed for failing two alcohol breath tests.
'Out of touch'
"We will not be swayed by it as we will never compromise on the safety of our customers and staff. You wouldn't let someone who had been drinking alcohol drive your family in a car, and we don't let people who have been drinking alcohol drive people's families in Tube trains.
"For the RMT leadership to announce a strike regardless shows how completely out of touch they are, just as the timing demonstrates that they know they have very little support from their members on this issue."
Members voted by 299 votes to 221 to take action. The turnout was 42%.
LU said the number of drivers who had voted to take strike action represented 8% of all drivers.
In December, RMT workers held a 24-hour strike on the Northern line over the same issue.