The PSNI said about 200 people gathered to protest at the opening of a private sexual health clinic in Belfast.
Among the services being offered by the Marie Stopes clinic are medical abortions, in line with current legislation in Northern Ireland.
The Stop Marie Stopes Campaign is being organised by the Northern Ireland based group Precious Life.
The protest began this morning close to the offices of the new clinic on Belfast's Great Victoria Street.
Terminations can only be carried out in Northern Ireland in cases where continuing the pregnancy would have a serious, permanent or long-term effect on the physical or mental health of the woman.
Women who meet these criteria, including those from the Republic of Ireland, will be able to avail of medical abortions at the clinic.
The centre's health professionals will make the necessary assessments, although the views of the woman's own GP will be taken into consideration.
Speaking in Stormont earlier this week, Northern Ireland Health Minister Edwin Poots said the law on abortion is "clear" and that his department will ensure the clinic complies with current legislation.
He also said he is opposed to any extension of the rule governing abortion in Northern Ireland and did not think there is "an appetite for abortion on demand".
Elsewhere, Labour Senator Ivana Bacik has told the Seanad that colleagues had criticised the opening of the clinic this week.
Senator Bacik said the clinic had said it would be operating within the law for women seeking to terminate pregnancies and that at least it is facing up to a reality for many thousands of Irish women.
She said about 4,000 women from the Republic still go to the UK every year for abortions.