BRUSSELS—Companies may ban Muslim employees from wearing a headscarf under certain conditions, the European Union’s top court said on Thursday in a ruling on two cases brought by women in Germany who were suspended from their jobs for wearing one. The issue of the hijab, the traditional headscarf worn around the head and shoulders, has caused controversy across Europe for years and underlined sharp differences over integrating Muslims. In the cases brought to court, both Muslim women—a special-needs carer at a childcare center in Hamburg run by a charitable association, and a cashier at the Mueller drugstore chain—did not wear headscarves when they started in their jobs, but decided to do so years later after coming back from parental leave. They were told that this was not allowed, and were at different points either suspended, told to come to work without it, or put on a different job, court documents …