The group, which hails from Russia and the UK, has damned Foster's proposals for 'New Holland' island as 'international trophy Modernism'.
In a letter printed in Saturday's Daily Telegraph, the five Classicists have combined forces to pan both Foster and Modernism at large.
The letter claims that 'of all sites [in St Petersburg], New Holland might be thought least capable of digesting the disruptive assertions of international trophy Modernism.'
The group adds that New Holland is an 'exemplary Classical ensemble' and that there was no reason not to build on 'its own Classical traditions and achievements' instead of opting for the Modernist alternative.
The Classicist coalition includes Classical City Online editor Anton Glikin, Art Watch UK director Michael Daley and St Petersburg Academy of Fine Arts professor of restoration Anatoly Alioshin.
They are joined in their diatribe - which labels Foster's selection as 'a counsel of despair' - by Legislative Assembly of St Petersburg deputy Alexey Kovalev and Cambridge University Architecture History professor David Watkin.
Foster and Partners was unavailable for comment at the time of going to press.
St Petersburg's authorities announced the appointment of Foster and Partners in February.