A smoking ban in all Northern Ireland government departments has come into effect.
Many have called for a universal ban in Northern Ireland
The ban sees smoking facilities removed and staff forbidden to light up on site.
Prisons will be exempt from the ban.
Since the end of March, smoking has been illegal in workplaces, including pubs and restaurants in the Republic of Ireland.
It was the first country in the world to introduce such a nationwide ban.
Many in Northern Ireland, particularly doctors and politicians, have called for a universal ban.
Earlier this year, it was revealed Northern Ireland could be the pilot area for a smoking ban in workplaces across the UK.
It is believed discussions have already taken place between ministers at Stormont and officials of the Department of Health in London.
The Civil Service in Northern Ireland has had a formal policy on smoking in the workplace since 1987.
This was revised in 1994, when the decision was taken that smoking would no longer be permitted in premises occupied by staff, except in designated smoking rooms or areas.