The Scottish Secular Society has blasted a job advert by Dundee Foodbank which said the position was only available to "a committed Christian and church member".
The Dundee Foodbank runs five centres in the city and posted the advert for a new manager on Facebook, which immediately received critical comments.
Citizens Advice says it is against the law to only offer jobs to a specific faith group, but it is acceptable to suggest that applicants belong to a certain religion if it will be an important part of the job.
However, in some cases, if an organisation can prove it is a necessity that the job holder be of one particular faith, it can be deemed legal.
The Scottish Secular Society wants the group to change the advert and slammed it as an "insult to thousands".
Chair, Spencer Fildes, said: "Whilst we applaud the work that Dundee Foodbank do, we do not applaud the closed shop employment policy they hold against those of other faiths and none.
"There is no law in this land that allows an employer to openly discriminate against those of a particular faith, yet here we have another example of discrimination towards other beliefs and those of no faith.
"Dundee Foodbank is closely linked with Tesco: imagine the outcry if the supermarket chain started advertising jobs for everyone but excluded Christians."
"What Dundee Foodbank, and it is not obvious they are a Christian organisation, are effectively inferring is that unless you are a Christian, you are unfit for the role. This is an insult to the thousands of non-Christians who hold charitable roles across the country."
Dundee Foodbank responded to online criticism by posting: "Dundee Foodbank is a Christian organisation, and elements of the role include Christian leadership, hence the church links requested."
In a statement Ewan Gurr, Scotland Network Manager for the Trussell Trust, said: "In my experience, the role of a Trussell Trust foodbank manager necessitates the delivery of duties such as leading church services, speaking to a number of church groups, working with predominantly church-based stakeholders and, in some cases, leading prayers.
"To be expected to carry out these responsibilities without being open and transparent about the need for them could be deemed to be equally as, if not even more, inappropriate than appointing someone to a position in which they feel uncomfortable or are expected to deliver in areas that may conflict with their own values.
"I expect Dundee Foodbank would not wish to put any employee in such a position, which is why the advertisement has been very clear about their desire that the successful applicant be a person of Christian faith.
"However, the foodbank continues to welcome the support and involvement of people from all backgrounds in its work to alleviate hunger for people in crisis."