Most shopworkers oppose the government's decision to suspend Sunday trading laws for eight weeks during the Olympic Games this summer, according to a new report.
The Usdaw union said a survey of over 20,000 of its members revealed that more than three out of four were against the move, with only 12% in favour.
Almost half of those questioned said they already faced pressure from their employer to work on Sundays, with almost three quarters feeling they would face added pressure if shops were allowed to open longer on a Sunday, the Press Association reported.
Usdaw met business minister Mark Prisk to outline why the union could not support the suspension of Sunday trading laws from July.
General secretary John Hannett said: "Shopworkers have once again made it clear that they oppose any further deregulation of Sunday trading and today we have made sure the government has heard the reasons why.
"Our members don't want to lose the one day they get to spend some quality time with their families and they quite properly fear the very detrimental impact deregulation would have on their caring responsibilities and their ability to maintain any semblance of work-life balance.
"Our opposition has nothing to do with being anti-Olympics. Usdaw supports the Olympic Games and it is a matter of huge pride that the UK has been given the honour of hosting them.
"We hope that the whole country joins in the celebration of sport and to that end we want as many of our members to be able to enjoy the Games with their families on the most important family day of the week."
Mr Hannett said the plans were "ill-thought through and rushed", adding there there was no evidence that extending Sunday opening hours will boost the economy or tourism.
He also complained there had been little meaningful consultation with employers and employees.
A Department for Business spokesman said: "Retail workers already enjoy strong employment protections around Sunday working, which are not shared by other sectors.
"Workers will keep all these protections, including the right to opt out of Sunday working, so no employees will be forced to work a Sunday during the suspension.
"Usdaw have raised some valid concerns about the Sunday Trading Laws suspension, which is why government is holding discussions with the unions, retailers and employers' groups before the second reading of the Bill.
"The Bill, which was announced in the Budget, proposes to suspend Sunday trading laws only temporarily."