Faith schools in Britain are to be investigated by the European Commission after complaints that they discriminate too widely on religious grounds when recruiting staff.
They will be scrutinised to see if expressing a preference for religious teachers - and having the right to pay them more than non-believing colleagues - breaches equality laws.
European Union rules state that a school must be able to prove a "genuine occupational requirement" in order to discriminate in favour of a religious candidate. However, the British Humanist Association (BHA), whose complaints sparked the inquiry, says that describing religious adherence as "desirable" falls short of this standard.
"If religious practice is a `desirable' quality and not an essential one, then it cannot be a genuine occupational requirement," Richy Thompson, campaigns officer at the BHA, told TESS. "It should either be essential or not there at all."
The vast majority of Scotland's state-funded faith schools are Catholic institutions, of which there are 366. Education legislation allows the Catholic Church to take religious belief into account when teachers are being recruited - that right has remained in place despite being challenged by teachers at employment tribunals in Glasgow in 2006 and 2012.
Michael McGrath, director of the Scottish Catholic Education Service, said: "We have been assured that Scottish councils are complying with EU legislation and the UK Equality Act in following the requirements set out in the 1980 Education (Scotland) Act when appointing teachers to denominational schools."
A Scottish government spokesman said: "We are confident that the current arrangements comply with UK and EU equalities legislation. The Scottish government will liaise with the UK government in any response required to the EU in respect of concerns relating to the employment of teachers in Scottish schools."
The BHA has asked the commission to investigate whether government guidance, which allows faith schools to discriminate on religious grounds when appointing teaching staff, is at odds with the EU directive.
The European Commission placed a similar investigation on hold last year after ruling that no evidence had been provided of "incorrect application of the laws at stake". However, the commission has agreed to reconsider the case after the BHA's submission of job advertisements as evidence.
Papers obtained by the BHA through the European equivalent of a Freedom of Information request show that the British government told the commission it believed a school could "give preference [to religious candidates] in respect of appointment to any teaching position" if that school could prove it had a "genuine and substantial religious ethos".
A spokesman for the commission confirmed that it was considering the complaint and had made contact with the British authorities.