Transport for London (TfL) warned of "significant" disruption, saying the strike will hit services from 4am, as well as affecting night buses into Friday morning.
Unite accused TfL of undermining efforts to resolve the row by making "misleading" comments about the dispute.
Regional officer Wayne King said: "TfL should be playing a constructive role in facilitating a resolution to the dispute with London`s 18 bus operators, who despite our tireless efforts over two years are refusing to talk collectively about ending pay inequality.
"Instead TfL is seeking to inflame the situation and undermine hopes of resolving the dispute with misinformed and misleading comments.
"All we are asking for is a collective forum to discuss how we can end pay disparities over a sensible time frame.
"Just as you wouldn`t employ police officers on different rates of pay across London neither should you with bus drivers."
Unite said there were hundreds of different pay rates for bus workers in London, with differences of up to £3 an hour.
Mike Weston, TfL`s director of buses, said: "I am very sorry that the leadership of Unite is intent on disrupting the journeys of London`s 6.5 million daily bus passengers, especially given that only 16% of bus drivers voted for strike action.
"Bus driver rates of pay have been negotiated and agreed between Unite and the bus companies individually under a long-standing and jointly agreed process. This has regularly resulted in pay rises above the rate of inflation.
"As in all professions, bus drivers have different levels of experience and it is only right that this can be reflected in pay. A `levelling up` of pay to the highest rates would result in higher fares and cuts to bus services for passengers and fewer jobs for bus drivers."
The strike was likely to mean "significant disruption to bus services", Mr Weston said, continuing: "I urge customers to please check our website for the latest news. We`ll be getting up-to-date information to customers as quickly as possible to ensure that they can continue to get around the city."
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