New research by the shop workers' trade union Usdaw shows 91% would be against the Government plans to relax the current laws.
The survey of over 10,000 workers has been passed on to the Department of Business, Innovation and Skills.
What the change means
Stores over 280 square metres in England and Wales are only allowed to open for six continuous hours on a Sunday.
Powers devolved to local authorities for them to decide if they wish to extend the hours.
Usdaw General Secretary John Hannett said: "Our members in large stores remain absolutely opposed to extended Sunday trading. The number one reason for their opposition is the detrimental effect this would have on their family life. They also cited real concerns about the additional pressure they would come under to work on Sundays if shops are open longer.
"Many shop workers, particularly parents, told us how important Sunday is to them and their family. Often it is the one day of the week when everyone can sit down together for a meal, with many saying they needed the time on Sunday to help their children prepare for the school week.
"The Sunday Trading Act is a great British compromise, which has worked well for over 20 years and gives everyone a little bit of what they want. Retailers can trade, customers can shop, staff can work; whilst Sunday remains a special day, different to other days, and shop workers can spend some time with their family."
A consultation on the plans closed last week with many church groups taking part to raise their opposition.
Speaking about the proposals, campaign group Christian Concern said: "A day of 'shared rest' is built in to God's design for creation, for the good of all.
"Erosion of Sunday trading restrictions will make it harder for some families to spend time together. It may also make it harder for some people to attend church."
Despite the government writing to Church of England bishops to ask for the support, the Church is continuing to speak out against the plans.