The Mayor of London has described a planned strike by tube staff as “bonkers”, “potty”, and “nuts.”
It comes as after the dismissal of a colleague who failed a random breath test and lost their job as a result.
Members of the Rail, Maritime and Transport union have voted 229 votes to 221, to go on strike.
Speaking to LBC during his tour of America, Boris Johnson said it was intolerable that the walkout was supported by just 24 per cent of those who voted.
In defence of the driver, the RMT Unions has said the current system does not offer safeguards to those with disabilities or who are on certain diets.
The RMT union leaders say the test was faulty as the driver was diabetic.
The Regional Organiser, John Leach said: "One of London Underground’s own doctors conceded that type 2 diabetes, liver disease and even fasting can give false positives on hand held machines."
Underground bosses say they have a zero tolerance approach to alcohol and drugs.
Mr Johnson stated his allegiance with TfL but said that it is perfectly right that someone who fails a breath test twice wouldn't be allowed to drive a train.
On the subject that only 42 per cent of those eligible to vote actually cast a ballot in the union proposal to strike, he said: "This is absolutely mad - only 299 people voted for this thing. It is bonkers, it is potty, it is nuts.”