LONDON - About 20,000 London Underground workers are expected to take part in a strike late afternoon on Wednesday, while Underground services in the capital will shut down.

The Independent described the strike as "the biggest London Underground strike in more than a decade".

Members from the National Union of Rail, Maritime and Transport Workers (RMT), one of the largest transport trade unions in Britain, and Transport Salaried Staffs Association (TSSA), train divers' union Associated Society of Locomotive Engineers and Firemen (ASLEF) and trade union Unite, plan to launch their strike as from 6:30 p.m. local time (1730 GMT).

"Due to the strike, customers are advised to complete their Tube journeys by 6:00 p.m. on Wednesday, and to travel earlier if possible," Transport for London (TfL) said.

It warned that Tube services would be exceptionally busy between 4:00 and 6:00 p.m. on Wednesday and would stop running after this time. There will be no service at all on Thursday.

In addition, First Great Western, a major train company in Britain, will stop its service between Paddington and Greenford stations for 48 hours as from 6:00 p.m. on Wednesday.

Reports were that the cause of the strike was because London Underground and union leaders failed to make an agreement on a pay increase when a 24-hour Tube service is launched in September.

Local media said the final offer of London Underground, which included a two percent pay rise and a 2,000-pound bonus (3,073 U.S. dollars) for drivers working nights, was rejected by representatives from four unions.

To cope with traffic chaos, TfL said around 200 extra buses, extra cycle hubs, and more cycles would be available, but public transport and roads would be much busier than usual.

TfL said travel ambassadors and volunteers would be handing out maps at transport hubs in central London and helping Londoners find alternate ways to get around.