The Scottish Government could face a legal challenge over its controversial decision to allow women to take abortion pills at home.
While pro-choice campaigners welcomed the move, the Society for the Protection of Unborn Children (SPUC) Scotland are fiercely opposed and are now consulting lawyers.
Chief executive John Deighan branded the decision "highly irresponsible" and claimed ministers may have "recklessly exceeded their powers".
Scotland's Chief Medical Officer, Dr Catherine Calderwood, recently confirmed she had written to all health boards north of the border to say that the drug misoprostol could be taken by women outside a clinical setting.
Dr Calderwood said it was "significant progress" that women in Scotland who are up to nine weeks pregnant could take the second dose of the drug at home if they wanted, saying this would allow them "more privacy, more dignity".
Campaign groups including Engender, Amnesty Scotland and Rape Crisis Scotland have welcomed the move, while Professor Lesley Regan, president of the Royal College of Obstetricians and Gynaecologists (RCOG) described it as "admirable".
But Mr Deighan claimed: "This is a highly irresponsible decision which threatens an explosion of bad mental health outcomes for women in Scotland.
"There are serious concerns that the Scottish ministers may have recklessly exceeded their powers and that their decision-making process is deeply flawed."
He added that the decision-making process in advance of the announcement had been "completely opaque" and there were also a "number of human rights aspects" SPUC is considering.
Mr Deighan said: "We have consulted with senior lawyers and experts in the field and we have some immediate concerns that will be rigorously examined in the coming days.
"The Scottish Government should be under no illusions. We will pursue the matter vigorously. If that means action through the courts, we will pursue it as far as necessary."
He claimed allowing women to take misoprostol at home represented a return to "DIY abortions", and warned these would be a "much greater threat to mental health".
He accused the Government of "spending taxpayers' money damaging women and practising abortion in a way far beyond what was ever imagined when the Abortion Act was passed" 50 years ago.
Mr Deighan added: "We have no alternative but to scrutinise every aspect of this decision and its implications for the sake of justice and fairness."
A Scottish Government spokesman said: "Abortion can be an emotive subject and the Scottish Government is working hard to ensure women are always able to access clinically safe services.
"Women will only be offered the opportunity to take misoprostol at home when clinically appropriate. The decision allows women to be in control of their treatment and as comfortable as possible during this procedure.
"Ministers are utilising an existing power available to them within the Abortion Act 1967. This is not a change to abortion law, and has been done following extensive clinical guidance led by the Chief Medical Officer."