The New York Landmark Preservation Trust said it was so concerned about the Upper East Side plans that it would extend its consultation for a further fortnight.
The London-based practice wants to build a 25-storey, elliptical tower above the much-remodelled Parke-Bernet Gallery building.
The plan includes recreating the original 1950s roof garden and creating new gallery space.
However, unlike Foster's highly acclaimed Hearst Building, the scheme has been greeted with anger from locals ( see AJ 19.10.06).
Speaking at a public meeting on Tuesday evening, Madison Avenue resident William Kahn likened the tower to the British invasion of New York during the American Revolution. 'We all remember the outcome of that,' he said. 'This is not evolution; this is revolution.'
The New York Landmark Preservation Trust is one of the few US conservation organisations with real influence and its recommendations about the Foster building will have a big impact on the proposal's prospects.
Another opponent, Elizabeth Ashby of the Defenders of the Historic Upper East Side, complained that the scheme was out of context.
'Vertical, glass and circular; masonry, rectangular and horizontal. There is no relationship whatsoever,' she told the meeting.