The UK's highest court has told two Catholic midwives they do not have the right to avoid supervising other nurses involved in abortion procedures.
The Supreme Court in London ruled that Mary Doogan and Connie Wood should have to support staff who are caring for patients having terminations.
The midwives previously won their case at the Court of Session in Edinburgh.
NHS Greater Glasgow and Clyde's appeal said the right to abstain should only extend to treatment ending a pregnancy.
Ms Doogan, from Garrowhill in Glasgow, and Mrs Wood, from Clarkston in East Renfrewshire, were employed as labour ward co-ordinators at the Southern General Hospital in Glasgow.
They challenged whether NHS Greater Glasgow and Clyde (GGC) could require them to delegate, supervise and support staff who were involved in carrying out abortions.
The Court of Session in Edinburgh initially ruled in 2012 that their human rights had not been violated as they were not directly involved in terminations.
At the time, judge Lady Smith said: "Nothing they have to do as part of their duties terminates a woman's pregnancy.
"They are sufficiently removed from direct involvement as, it seems to me, to afford appropriate respect for and accommodation of their beliefs."
But last year, appeal court judges overturned Lady Smith's judgement, ruling the "right of conscientious objection extends not only to the actual medical or surgical termination but to the whole process of treatment given for that purpose".
NHS GGC later asked the Supreme Court to examine whether section 4(1) of the Abortion Act 1967, which provides that "no person shall be under any duty... to participate in any treatment authorised by this Act to which he has a conscientious objection", extends to labour ward co-ordinators.
Eleanor Bradford, BBC Scotland Health Correspondent
The Abortion Act of 1967 gives staff the right to conscientiously object to participating in abortions - the question at the centre of this case was: What constitutes participation?
Mary Doogan and Concepta Wood wanted to be absolved from anything which led to a termination, including managing junior staff who were treating women having terminations.
Their employer, NHS Greater Glasgow and Clyde, argued that this would make staffing a hospital impossible, and that it was not unreasonable to ask them to carry out managerial duties.
What is surprising is that there have been so few challenges over more than four decades to this section of the Abortion Act. This judgement brings some clarity to what has been a grey area.
The Supreme Court decided that the right to conscientious objection did not extend to the the labour ward co-ordinators.
Lady Hale, Deputy President of the Supreme Court, said: "Parliament will not have had in mind the hospital managers who decide to offer an abortion service, the administrators who decide how best that service can be organised within the hospital, the caterers who provide the patients with food and the cleaners who provide them with a safe and hygienic environment.
"Yet, all may be said in some way to be facilitating the carrying out of the treatment involved.
"The managerial and supervisory tasks carried out by the labour ward co-ordinators are closer to these roles than they are to the role of providing the treatment which brings about the termination of the pregnancy. 'Participate' in my view means taking part in a 'hands-on' capacity."
Reacting to the judgement, Ms Doogan and Ms Wood, said: "We are both saddened and extremely disappointed with today's verdict from the Supreme Court and can only imagine the subsequent detrimental consequences that will result from today's decision on staff of conscience throughout the UK.
"Despite it having been recognised that the number of abortions on the labour ward at our hospital is in fact a tiny percentage of the workload, which in turn could allow the accommodation of conscientious objection with minimal effort, this judgment, with its constraints and narrow interpretation, has resulted in the provision of a conscience clause which now in practice is meaningless for senior midwives on a labour ward."
The Society for the Protection of Unborn Children (Spuc), which funded the midwives' case, said it could lead to senior staff leaving their roles.
Paul Tully, general secretary of Spuc, said: "Junior midwives might still be able to work in labour wards where abortions are performed but they will be restricted to 'staff midwife' status at best.
"They could easily be placed in an impossible situation by pro-abortion superiors, and would be unable to receive promotion to a more senior role without fear of being required to violate their consciences.
"This will affect anyone who objects to abortion, of any religion or none."
The health board's appeal was backed by both the Royal College of Midwives (RCM) and the British Pregnancy Advisory Service (BPAS), which said they were "deeply concerned" at the right to conscientious objection being extended.
Ann Furedi, chief executive of BPAS, welcomed the ruling and said: "BPAS supports the right to refuse to work in abortion care, not least because women deserve better than being treated by those who object to their choice. But the law as it stands already provides healthcare workers with these protections.
"Extending this protection to tasks not directly related to the abortion would be to the detriment of women needing to end a pregnancy and the healthcare staff committed to providing that care.
"There are enough barriers in the way of women who need an abortion without further obstacles being thrown in their way."
Gillian Smith, RCM director for Scotland, said: "This ruling is sensible and both women and midwives will welcome it.
"The ruling gives extensive definition to complex clinical and other situations, in regard to whether conscientious objection applies or not.
"Midwives and other clinicians will benefit from this ruling's clarity and women will be able to continue to exercise their choice over their reproductive rights."