Shops that employ both men and women in Saudi Arabia must build walls at least 1.6m high to separate the sexes.
Authorities have said separation walls must be built to enforce segregation laws within the country, local media said.
Labour minister Adel Faqih ordered the walls. The move was confirmed by Abdullatif al-Sheik, the head of the Commission for the Promotion of Virtue and Prevention of Vice.
In December, the head of the religious police criticised the labour ministry, saying some women who work in shops are harassed and did not have a good working environment.
Saudi Arabian women long complained about having to buy lingerie from salesmen before male floor staff were banned from such stores in 2011 and replaced with women-only staff.
Basic human rights denied
That led to the creation of more than 44,000 jobs for women and dented the high female unemployment rate of 30 percent.
Sex segregation is already strict in restaurants, as women have to remove their veils to eat. Women must sit in family areas of restaurants, which also have "bachelor" areas for single men. Women cannot eat in restaurants unaccompanied by a man.
Farida Deif, women's rights researcher for the Middle East at Human Rights Watch, said: "The Saudi government sacrifices basic human rights to maintain male control over women. Saudi women won't make any progress until the government ends the abuses that stem from these misguided policies."