The international star has joined fellow peer Richard Rogers on the list of those backing the reform group in the forthcoming election.
But the move is particularly unusual for Foster, who has traditionally steered clear of overtly political statements.
The group, which has eight committed reformers standing for the seven seats reserved on the board for members of the profession, has mounted a campaign to sign up high-profile supporters in the past few days.
The reformers have this morning also confirmed the support of Jonathan Adams, the design director of Capita Percy Thomas.
Foster and Adams join a growing list of backers, which includes Terry Farrell, Amanda Levete, of Future Systems, and Piers Gough, of CZWG.