Burger King is seeking an agency to cover the chain's UK and Ireland consumer PR and launch a fresh brand-building campaign.
One source estimated the lucrative brief to be worth in excess of £200,000 a year.
It is understood that Burger King has requested creds from a shortlist of agencies, which will go through to face-to-face meetings before a pitch process.
Burger King plans to hire the new agency by 1 January 2012.
The company's move away from Cow comes after a wave of changes in its broader UK marketing team. These form part of the chain's aim to create a single global brand marketing and operations function.
It also comes as the firm ditches brand character 'The King' in the UK, to focus more on its food credentials.
Helena Smales, EMEA comms manager, joined just over a year ago, having previously worked on the Burger King account at Cow PR.
Smales told PRWeek: 'Over the past six years, Burger King UK and Cow PR have enjoyed a collaborative partnership that resulted in many successful campaigns for the brand. Burger King thanks Cow for their many years of service.'
In 2009 Cow ran a PR campaign around the world's most expensive burger, priced at £95 and made of Kobe beef, saffron, truffles and pata negra.
Last month Burger King was among a group of fast-food brands that agreed to display calorie information on its menu boards in the UK as part of the Government's 'responsibility deal', which signs up companies to help tackle social problems.
Cow PR is working its three months' notice, which is due to end in mid-December.
- In October 2010 Burger King Corp was bought by global investment firm 3G Capital in a deal valued at £2.1bn.
- The firm failed to make Interbrand's Best Global Brands 2011 report this week. It last appeared in 93rd position in 2009. McDonald's is sixth.
- Burger King opened its first UK restaurant in 1977. It now has around 500 restaurants in the UK and Ireland.