The unlisted Art Deco shop is set to be demolished to make way for a nine-storey student accommodation block designed by the practice.
But campaigners Huddersfield Gem, along with local residents, claim to be preparing a campaign to keep the building.
Designed by Co-operative's in-house architect W A Johnson in 1937, the former Co-op has been described by architect and Gem member Adrian Evans as, 'the first and best example of a truly Modern building in Huddersfield.'
It was assessed for listing in 2005 but failed, despite another of Johnson's buildings, the Bradford Co-op, recently being listed Grade II.
Evans added: 'It would be an outrage to lose it and have it replaced by a mundane nine-storey block.'
David Harward, of Ssharc, defended the proposals, claiming the abandoned building had been badly neglected and that refurbishment was no longer a viable option. He said: 'The stone cladding is only being held up by goodwill.
'This building has a lot of defects and it would be far too expensive to get it back to its original state.
'I live locally and I love the building. But a refurbishment just doesn't stack up financially and its size and shape doesn't lend itself to reuse for, say,student bedrooms.'
Ssharc's proposals are currently lodged with Huddersfield council and are awaiting the go-ahead.