Female employees in Gambia's public sector have been ordered to cover their hair during working hours, according to a presidential directive circulated to staff this week.
All female staff have been ordered to use "a head tie and neatly wrap their hair with immediate effect," said the directive from President Yahya Jammeh, who declared the West African country an Islamic republic last month.
"All are strictly advised to adhere to this new directive," it said, while advising department heads to implement it.
The order did not create exceptions for non-Muslims.
In 2013, a presidential directive gave public sector workers Fridays off to allow the mainly Muslim population more time to attend mosques.
Jammeh has implemented strict rules against homosexuality and on the media since taking power in a coup in 1994.
Gambia is one of the world's poorest countries with 48 per cent of its 1.9 million people living in poverty and a life expectancy of 59, according to the World Bank.
Islam is believed to be practised by about 90 per cent of Gambia's population, but it had been a secular state since its independence in 1965.
The country is due to hold a presidential election on December 1.