A company is planning to introduce a "period policy" to allow female staff to work flexibly around their menstrual cycles.
Co-Exist in Bristol says women will be allowed to take time off during their period and make up the time later.
Director Bex Baxter told the Bristol Post she had seen women at work "bent over double" in pain but unwilling to go home which was "unfair".
Menstrual leave exists in Japan, parts of China, South Korea and Taiwan.
It is thought the company is one of the first firms to introduce it in the UK.
Miss Baxter said criticism of menstrual leave came "from a place of fear".
She told the BBC: "Women don't want to feel they are less employable than men if they are taking time off [for periods]."
Co-Exist employs 24 people, seven of them men. Ms Baxter said the details of the policy had not yet been worked out but would be discussed at a seminar later this month.
She said there would inevitably be a fear of lack of fairness or of women taking time off "willy nilly" but added: "We want to create a policy that trusts people - we don't want to create something that... doesn't recognise the needs of the business."