Passengers were warned of disruptions due to the strikes of thousands of bus drivers London will affect routes for seven days in December.
Drivers in Unite The union of two employers, Abellio and Metroline, will strike for three days from Thursday 1 to Saturday 3 December in a dispute over pay.
Transport for London (TfL) said customers in north, west and south London should check information before traveling and allow extra time for their journey.
While some commuters have subway and train alternatives, with more than 100 routes suspended, road and bus congestion that remains is likely to be significant.
The latest Acas talks between Unite and Metroline are due to take place on Wednesday, with the union still negotiating with Abellio.
Metroline workers serving routes in north and west London are due to strike again on December 8-9 and 15-16.
Abellio bus workers, mainly based in the south and west of the capital, went on strike for three days at the end of November and will also strike on December 9-10 and 16-17.
The last action of bus drivers on both companies will coincide with RMT railway strikeswhich may also affect some Tube, London Overground and Elizabeth line services in west London.
Thousands of RMT members working for Network Rail and 14 rail companies will strike twice for 48 hours a week. The first strikes, on December 13-14 and 16-17, will cause disruption for six consecutive days in the run-up to Christmas, with similar impacts on services through subsequent strikes on January 3-4 and 6-7.
Unite general secretary Sharon Graham described Metroline, owned by Singapore-based ComfortDelGro, and Abellio as “extremely wealthy companies” that could afford to pay drivers the same as others in the capital.
Louise Cheesman, Director of Buses St TfL, said: “We apologize for any disruption caused to Londoners, particularly for people in west London who may be affected by both sets of strikes. People will still be able to travel in the affected areas, but other routes may be busier than usual.
“We encourage everyone in these areas to plan ahead, check before traveling and allow more time for travel.”