Organised by the Keep Sunday Special campaign, constituents were invited to Westminster to meet their MP and discuss the issue.
The government wants to change Sunday trading laws so local councils can decide how long their large shops open on Sundays.
Currently they are restricted to just six hours trading but under the new laws stores could become 24/7.
Government ministers have responded to criticism from the Church by including a clause that will allow Christians to opt out of Sunday shifts with a months' notice.
The Keep Sunday Special campaign says this is not enough and workers will feel obliged to take shifts.
It has produced a database of MPs it thinks could be persuaded to vote against the proposals, which are included in the government's Enterprise Bill.
A number of Conservative MPs have also signalled their intention to rebel and vote against the government.
