Morocco says the law against proselytism applies to all religions
Morocco says it will take a tough line on proselytism - seeking converts from another religion - two days after it expelled 20 Christian workers.
Communications Minister Khalid Naciri warned that the government would be "severe with all those who play with religious values".
Religious freedom is guaranteed under Moroccan law but proselytism is banned.
Some Christian groups claim the authorities are deliberately trying to restrict their work in the country.
The expelled Christians had run a children's home called Village of Hope near the town of Ain Leuh in the Middle Atlas mountains.
The home housed 33 children who, it is claimed, would otherwise have been abandoned.
The 20 foreign workers were given just a few days' notice to cease their activities and leave the country, a statement on the group's website said.
They were accused of trying to convert the children in their care to Christianity.
The group's statement says it had always been open about its Christian beliefs with the authorities, and for 10 years had been allowed to take in and foster abandoned children.
It says the deportation is part of a nationwide crackdown against Christians living in Morocco and has appealed to the king to overturn the ban.
A British couple who live near Marrakesh and who know the Village of Hope children's home told the BBC they were stunned by the news.
The couple, who declined to be named, said the foster parents and the children - some of whom had lived at the home for 10 years - had been left traumatised by the separation.
Mr Naciri said the expelled foreigners "took advantage of the poverty of some families and targeted their young children, whom they took in hand, in violation of the kafala (adoption) procedures for abandoned or orphaned children".
He said Morocco had "always been and remains a land of openness and tolerance".
"All churches have their place on the street in Morocco and Christians practise their religion freely," the minister said.
"The rare cases of expulsion have nothing to do with the practice of Christianity but with acts of proselytism."
He said the warning also applied to Muslim groups.
BBC religious affairs correspondent Christopher Landau says under Moroccan law, Jewish and Christian minorities can worship without restriction but are not allowed to encourage citizens from the Muslim majority to abandon their faith of birth.
However, some missionary groups in the country claim authorities are deliberately trying to restrict Christian work, he adds.