Thorntons wants an agency to help increase consumer awareness between the peak times of Valentine's Day, Easter, Mother's Day, Halloween and Christmas, to drive sales throughout the year.
The chosen agency will be charged with presenting the chocolate-maker as a premium brand to help it stand out from supermarket rivals.
The chocolate-maker and retailer announced at the beginning of March that it would shut a further 60 stores after poor first-half results, bringing the total number of planned closures during the next three years to 180.
The cull of stores is part of a strategic review to shave £1m off the company's annual rent bill, as it struggles to compete with supermarket confectionery prices.
The consumer brief is currently handled by Salt PR, which is repitching. The agency was hired in 2008 to deliver PR support during the brand's peak annual trading periods.
Thorntons UK PR manager Emma Tagg confirmed the pitch process was taking place, stating that since appointing Salt PR in December 2008 'this is the first time we have repitched the contract'.
The firm also uses Nudge to handle high-end food publications and bloggers, but this brief is not affected.
Thorntons has asked for written proposals from a shortlist of agencies with pitches planned for the beginning of April. Interested agencies have been asked to submit written proposals to a procurement company for fees of £3,000, £5,000 and £7,000 a month.
The remit would include the running of the Thorntons press office, but not its social media activities, which will remain in-house.
Thorntons currently has 379 of its own stores and 200 franchise stores across the UK, employing more than 3,750 people.