The 20th Century Society – whose remit includes buildings erected since 1914 – publishes its Buildings at Risk list every two years. The last edition in 2019 included Waterloo's BFI IMAX.
The 2021 list – published in the week of the elections for the Mayor of London and London Assembly – features in second place London's City Hall.
The Foster & Partners building is just 19 years old. It is not yet known what City Hall's Kuwaiti landlords intend to do with the riverside building when the Greater London Authority moves to the Royal Docks.
Historic England is said to have rebuffed the society's application to have the building listed at grade II*.
Buildings less than 30 years old have to meet tighter criteria for inclusion on the national list of buildings of historic and architectural interest.
In December last year Mayor of London Sadiq Khan said: "I am sure that City Hall has a full life ahead of it, with the potential for a number of different incarnations.
"I am confident that good use will be made of the building for many years to come and that it will continue to have landmark status in the architectural vernacular of our city."