'Brands such as Cyberdog, which joined Upfront after we started work on the account, are a bit "Camden" while we are more "street",' said Spin head of press Kate Hyde.
The agency handles marketing and PR for clothing brands Benjamin Kirchhoff, Fenchurch and Firetrap.
'We had concerns about being associated with brands like Cyberdog and what that would do to our own brand integrity in the market,' Hyde added.
But in a statement issued to PRWeek through its new agency, Coalition Total Communication, Upfront head of marketing John Rowley said Spin failed to deliver 'key elements of our brief'.
'We require better strategic guidance and understanding of our business and brands as we move forward towards our second show in January 2006,' Rowley said.
Hyde insisted the agency had not been dropped but resigned the account.
Upfront was reportedly unhappy with lack of editorial coverage and visibility among clothing brands.
The inaugural show, organised by Elgin Events, takes place at London's Barbican Exhibition Centre on 3-4 July.
Other brands involved with Upfront include Russell Athletic and Rocawear, with BlackBerry one of its headline sponsors.