Taxi drivers organised by the United Private Hire Drivers branch of the IWGB trade union block traffic for several hours in protest of Sadiq Khan's new congestion charge proposals.

Private taxi drivers — some of whom work for firms like Uber — are taking legal action against the mayor of London over what they claim is a racially discriminatory congestion charge.

Sadiq Khan, the city's mayor, oversees transport authority Transport for London (TfL). From April 8, TfL will begin charging these drivers the new £12.50 ($15.22) daily fee levied on those who drive within the city's ultra-low emission zone. Under the old congestion charge rules, private hire drivers were not subject to the daily charge.

London's "black cab" drivers will remain exempt from the charges. In 2021, the area included in the zone will be expanded.

In a pre-action letter sent to the mayor's office, the IWGB (Independent Workers Union of Great Britain) argued that the charges will be imposed on a workforce where 94 percent of drivers are from ethnic minority backgrounds, while the majority white "black cab" drivers will avoid the costs.

The union claimed that this was a case of indirect discrimination under the U.K.'s Equality Act, and that the policy also breached a number of articles under the European Convention on Human Rights.

It has launched a croudfunder campaign to raise money for the legal costs to take on TfL in court. On Friday afternoon, the IWGB had raised £2,225 of its £50,000 target.

The IWGB has previously proposed alternatives to the charge, including a levy on operators such as Uber. Yaseen Aslam, secretary of the IWGB's private hire drivers branch, said in a press release on Friday: "We hope the mayor sees sense and scraps this policy that promises to push thousands of drivers into deeper poverty."

A spokesperson for the London mayor's office said in an emailed statement Friday that the number of private hire vehicles entering the congestion charge zone had risen from 4,000 a day to 18,000 a day since 2003.

"(The mayor) simply isn't prepared to ignore the damaging impact this has on congestion and increasing air pollution. Congestion has a crippling impact on businesses across the capital," the spokesperson said.

"Most other motorists, from private cars to small business owners, are liable for the congestion charge. Removing the exemption for private hire vehicles is a key part of our plans to both reduce congestion and to protect Londoners from harmful emissions from polluting vehicles."