Thousands of bus workers are to stage a 24-hour strike over pay tomorrow, causing travel chaos for passengers.
The walkout at three firms - First, Metroline and Metrobus - is expected to cause widespread disruption to services in London.
Unite has called the strike in support of a campaign for a single pay rate of £30,000 a year for a 38-hour week for drivers, arguing that pay in the capital's 18 bus companies varies by up to £6,000.
Unite officer Peter Kavanagh said: "There is a startling disparity between bus drivers' pay in the capital, with rosters in some companies seeing many drivers complete nearly 60 hours a week.
"Not only is this potentially unsafe, it is unfair to have bus workers across London doing the same job for less money or having to put in longer hours."
The dispute is set to escalate, with Unite balloting workers in other bus companies for industrial action later this month.
Adrian Jones, managing director of First bus company London & Berkshire, said: "The union is intent on dragging further bus companies into strikes in pursuit of its fruitless bid to standardise conditions of working and pay in all companies.
"Transport for London deal with each contracted operator separately and have given no indication that they would be willing to change the way in which routes are bid for to allow for a single pay structure.
"First's bus drivers are already amongst the best paid bus workers in London. Between 2003 and 2007, First's bus drivers' pay increased by 34%, during which time inflation has increased by only 16%. Most drivers receive over £25,000 a year and this rises to over £30,000 a year for a normal rostered week for over a quarter of drivers."