Convenience retailers believe that their campaign to preserve the current Sunday trading regime is building momentum following the ending of the government's consultation period last week.
In a letter to the Secretary of State for Trade and Industry Alan Johnson, ACS chief executive David Rae called on the government to take note of of the gathering wave of public opinion against liberalisation.
Rae said: "Over 200 MPs have signed an Early Day Motion opposing liberalisation of Sunday trading laws, and a recent poll showed that a large majority of MPs oppose changes to the Act. More and more newspapers are taking an editorial line against liberalisation."
The ACS has also called for a freeze on all policy discussions in this area for the duration of the expected investigation into the grocery market, which could take up to two years to complete.
The MPs opposed to liberalisation have been joined by Andrew Stunnel, the Liberal Demcocrat MP for Hazel Grove in Cheshire. Stunnel gave his views in a letter to Stockport-based wholesaler Steve Parfett.
He said: "It is quite clear that any regulation would essentially only be for the benefit of larger stores and to the detriment of small traders."
The campaign has also received support from an unlikely source in the shape of supermarket groups Morrisons and Sainsbury's. Morrisons told a cross-party panel of MPs that the changes would not be popular with its employees, while Sainsbury's said that its customers had not indicated they wanted Sunday trading liberalised.
C-Store helped to kick off resistance to changes in the law by commissioning a poll in November 2005. The study showed that 68% of the public opposed any changes. Of the 28% who were in favour of longer hours, half would oppose change if new legislation resulted in local shops going out of business.