Priti Patel's nationality and borders bill is a "potential racist" piece of legislation and should not go ahead, the London Assembly has said.
A large majority in the devolved chamber backed a motion calling on the Home Secretary to stop the controversial legislation and said it "places Britons of ethnic minorities as second-class citizens".
Under the law, the Home Secretary would be able to strip any British national of their citizenship "where they are deemed to have claim to citizenship of another country" and where there was a "public good".
Critics say the law creates a situation where millions of British citizens who either came to the country as immigrants or are recently descended from immigrants will not enjoy the same rights to keep their citizenship as others.
Other provisions in the bills would also increase prison sentences for refugees who try to exercise their right of asylum by travelling to the UK through unconventional means.
In a motion passed by 14 votes in favour to 8 against, the assembly said: "If this bill were to become law unamended, two in five people from ethnic minority backgrounds would become eligible to be deprived of their citizenship without warning and 6 million people across the UK, a proportion of whom will be Londoners, would be at risk of having their British nationality revoked.
"This Assembly believes that the law undermines equal citizenship for all and places Britons of ethnic minorities as second-class citizens [and] that the law is also an attack on the rights of refugees who potentially face a four-year prison term for not entering the UK directly from a country of persecution.
"Therefore, this Assembly calls on both the Chair of the Assembly and the Mayor of London to each write separately to the Home Secretary to express our condemnation of this Bill on behalf of Londoners."
It added that the assembly "believes it is a potentially racist, divisive piece of legislation which echoes the ongoing injustices inflicted on the Windrush generation".
Labour, the Greens and Liberal Democrats supported the motion while it was opposed by Conservatives. The vote took place on Thursday.
Labour assembly member for Ealing and Hillingdon, Dr Onkar Sahota AM, who proposed the motion, said the law could make "a huge swathe of Londoners second-class citizens".
“What makes London great is its openness and its diversity, but this Bill could see two in five people from ethnic minority backgrounds stripped of their citizenship with no warning," he said.
“This proposed two-tier system is deeply concerning and unacceptable and could make a huge swathe of Londoners second-class citizens in their country.
“The Government must learn the damning lessons of the Windrush Scandal and scrap this dangerous and divisive Bill.”
Supporting the motion, Hina Bokhari, a Liberal Democrat assembly member said: "It is wrong, this bill will risk normalising the racist and xenophobic attitudes that has risen since Brexit ... it will legitimise, quite simply, more hatred."
She said the bill was not reflective of London's values, adding: "London is not isolationist, it's not protectionist, it's not insular."
Tory MP Shaun Bailey, who did not support the motion, said many Tories were "very concerned about the notion of statelessness" but that he would not back the other assembly members because of the motion's "inflammatory language".
"Suggesting that the government is out-and-out racist I don't think is simply useful for the debate," he said.
But Green London Assembly member Zack Polanski, who supported the motion, said: "There are people dying right now in our seas: in the Aegean, in the Mediterranean, in the Channel and this could stop tomorrow if the government would just take action: all they need to do is to provide safe and authorised passage through those seas and we could give everyone a better future.
"I hope that one day people from these communities could be standing here as a London Assembly member giving these speeches."
A Home Office spokesperson said: “These are yet more inaccurate claims on the administrative changes to deprivation powers in the Nationality and Borders Bill.
“Removing British citizenship has been possible for over a century, and is used against those who have acquired citizenship by fraud, and against the most dangerous people, such as terrorists, extremists and serious organised criminals.
“This change in the Bill is simply about the process of notification and recognises that in exceptional circumstances, such as when someone is in a war zone, or informing them would reveal sensitive intelligence sources, it may not be possible to do this.”
