Brunswick has worked with William Hill since its 2002 flotation but has now been put on alert following the firm's decision to put its account out to pitch in the coming weeks.
The move is thought to have been triggered by the appointments of Lyndsay Wright as William Hill's first head of investor relations six months ago and Ralph Topping as chief executive last year.
Wright confirmed she had been in initial discussions with a 'large number' of agencies and said she was currently shortlisting for pitches to take place in the coming weeks.
Brunswick has been invited to participate in the process and a source at Brunswick confirmed to PRWeek that the agency was committed to repitching for the account.
The review is understood to include Brunswick's direct City competitors as well as some niche financial players.
Wright said: 'We have talked to all of the usual suspects and some unusual ones. We have come into the process with a very open mind about the best approach, but we are definitely looking for someone with a strong financial and City focus.'
Investor relations has previously formed a key part of Brunswick's existing brief with William Hill, thought to be worth a six-figure annual sum. But Wright's arrival is likely to result in downwards pressure on the firm's financial PR spend.
Wright said: 'The brief will certainly be different in the fact that we now have an in-house investor relations capability, but it is still a big brief given the corporate profile of William Hill and the media attention we tend to get.'
In February, Brunswick helped William Hill complete a £350m rights issue as it looked to reduce its debts.
'As a business we are at a very interesting point,' said Wright. 'Our new chief executive has made some significant changes in his first year, particularly around our online gambling service, which has been a big focus for City analysts and the financial media. With our acquisitions in this area now bedding in, we felt it was a good time for us to conduct a comms review and gear ourselves up for the next stage of development.'
The bookmaker played a key role in persuading Alistair Darling not to increase gross profits tax on the industry, but it could still move some of its operations overseas.
HOW I SEE IT
David Rydell, director, Bell Pottinger Corporate & Financial
Life is not easy for high street bookies. The spending trend for punters is to spend less and less often. This favours low-cost online operators and the rapid growth of web-based gaming shows that this is the new game in town. William Hill last year signed up leading gaming provider Playtech to launch William Hill Online and this is where its growth lies. Online is cheaper to run and lightly regulated. The high street bookie is not yet dead, but the revenue lines are being rewritten. The comms challenge is to ensure customers and investors understand why and support the inevitable evolution.