The president of Nottingham Secular Society has criticised the city council's decision to offer reduced parking charges for churchgoers.
Charges for on-street parking in Nottingham on Sundays and evenings were introduced in November.
After the city's churches complained charges would put people off, the city council introduced a £50 prepaid voucher book saving about £70 per year.
The secular society's Dennis Penaluna said everybody should pay the same.
"We believe that if there is a law or regulation... that law has to be applied equally to everybody," said Mr Penaluna.
"So when you get self-interested groups coming along, they shouldn't be given exemptions unless they are given to everyone else as well."
Dean of Nottingham's Catholic Cathedral, Father Geoffrey Hunton, said the church had lost 10% of its congregation since the new charges had been brought in, even with the prepaid voucher scheme.
"Initially there's a £50 outlay to purchase the ticket book. There hasn't been a great uptake and people are just a bit dubious about paying the £50 in this current economic situation," he said.
Measures introduced to support churches include discounted parking in multi-storey car parks and a reduced tariff for on-street parking for congregations of churches which are not located near car parks.
Mr Penaluna added: "People can have their faith, I encourage it, but they should not be given privileges because of their faith."
In a statement, Nottingham City Council: "New charges on Sundays and in the evenings are at a lower level than currently apply during Monday to Saturday.
"This recognises the need to balance the charges with the levels of demand.
"While the council has offered discounted parking to city centre church groups, consideration has also been given to those who visit the city centre for other reasons on Sundays."