Incumbent agency Praxis PR is believed to have been invited to take part in the pitch.
Lowman stressed the decision to repitch did not reflect the work provided by Praxis, but that after five years, the association felt a pitch was necessary to test the market.
'We are not dissatisfied with our present agency. We are finding out about the market and the options available,' he said.
The association has retained Praxis, led by chairman Chris Guyver, since December last year. Before that ACS employed Northern Lights for two years before the agency was acquired by Praxis. Prior to using Northern Lights the ACS used Politics International. Five years ago, ACS retained the then Ludgate Laud for PA work, before switching to Politics International.
The PA remit ACS is putting up for grabs includes monitoring, strategic PR advice and analysis, support and proactive campaign work.
The body is working on a number of PA campaigns, for example on the Government's Climate Change Levy, which taxes small businesses' use of energy.
The Government compensates small firms for the cost of the levy by cutting employers' national insurance contributions. This is a perk few convenience stores can benefit from, since they employ a disproportionate number of part-time staff who earn wages that fall below the NI contributions threshold.
ACS chief executive David Rae issued a public warning earlier this month to the Chancellor that if measures were not taken to address the impact of the Climate Change Levy, neighbourhood convenience stores could be financially crippled.
The PA role of representing convenience retailers to the Government is a core function within the ACS, leading the organisation to form a dedicated PA lobbying committee.
Other agencies retained on the ACS's roster include Tansor PR on a brief to raise awareness of the association in the grocery trade press.