Plans to appoint a named guardian for every child in Scotland are facing a legal challenge by a Christian group.
Last month, MSPs approved laws assigning children up to 18 a "named person", such as a teacher or health visitor, to look out for their welfare.
The Christian Institute has accused Holyrood of interfering with family life, and say the plans could flout human rights laws.
The Scottish government called the proposal "fair and proportionate".
It said parents would not be required to accept help or advice from the named person.
Even before it was passed, the named guardian element of the Children and Young People (Scotland) Bill attracted controversy.
Children's Minister Aileen Campbell said the legislation would stop vulnerable children slipping through the net and give families "somewhere to go if they need an extra bit of help".
Charity Children 1st supported the plan but religious groups, including the Church of Scotland, raised concerns around diminishing the role of parents.
Scottish Conservatives MSP Liz Smith, whose bid to amend the bill failed, said the plan would "tip the balance of family responsibility away from parents towards the state".
The Christian Institute, a campaign group which promotes family life and a literal interpretation of the bible, also strongly opposed the plan and lawyers for the group have written to the Scottish government saying they would seek a judicial review.
The group, which said it had raised £30,000 to pay for the action, accused MSPs of interfering with rights to a private and family life and said the plans could be in contravention of the European Convention on Human Rights (ECHR).
It has appealed to the government to delay enacting the legislation until after the case is heard.
Director Colin Hart said: "It is an invasion of the most grotesque nature which undermines the rights and responsibilities of ordinary mums and dads who are trying their best to raise their children in the best way they see fit."
A Scottish government spokesman said ministers were confident the legislation was compliant with the ECHR.
He added: "Families are not required to accept advice or offers of help from the named person.
"Any actions or advice from the named person must be fair, proportionate and respect rights with the aim of safeguarding the well-being of the child."