Business Secretary Sajid Javid said reviewed plans to allow shops to open longer on Sunday than the current six hours would include a religious clause.
That would mean a Christian could give one month's notice to their employer that they do not want to work on a Sunday.
The employer would then be legally obliged under law to remove that person from shifts on Sundays.
Michael Trend from the Keep Sunday Special campaign told Premier it wasn't a good enough safeguard: "The truth is if you work in a large supermarket and a lot of your mates are doing Sunday shifts it's quite difficult for you to let down the side, it's quite dificult for you to exercise these rights.
"So I don't think there's much to be said for that."
Mr Javid said the new powers would let councils 'zone' any relaxation so they will be able to prioritise high streets and city centres.
He added that the government will also strengthen the duty on employers to notify employees of their rights about working on Sundays.
"We are protecting those who do not wish to work Sundays, and those who do not want to work more than their normal Sunday working hours," he said.
Under the plans, local councils will have the ability to let shops open longer than the current restriction of six hours.
The government said authorities could pick and choose shops to benefit from the change so they could help struggling high streets.
Christian charity CARE said it remained unconvinced. A spokesperson told Premier some workers would inevitably face pressure from their bosses to work Sundays.
CEO Nola Leach said: "This is not just a religious issue. An opt-out for Christians is all well and good, but what about the Unions and small businesses who are hugely concerned by these proposals? The government are clearly trying to make it a religious issue when it is so much bigger than that."
Full results of a public consultation on the issue have yet to be published by the government.
John Hannett, General Secretary of the shop workers union Usdaw, said: "It is all well and good for the Government to highlight local authority responses to the consultation but, as it is now nearly five months after it closed, surely we should be allowed to see all responses.
"I hope the Government will publish in full the views of retailers, shop workers, community leaders and all those who take an interest in Sunday trading; so that MPs will be able to take full account of the consequences of future decisions on Sunday trading, particularly the impact on the retail trade.
"Their views are just as important as local authorities and should be heard as part of the debate."