All six massage salons in the local authority area of Haarlemmermeer have been closed down after they were found to be offering clients sex, the council said on its website.

One of the massage parlours may also have been involved in human trafficking and the police have been called in, the website said.

Mayor Marianne Schuurmans has closed the salons for a three month period. ‘It is illegal to offer sexual services for money without a permit,’ the mayor said in a statement. ‘In addition, not all the masseuses were doing the work out of free will. This is reason enough to tackle this form of illegal prostitution.

The council had used a plain clothes inspector to book appointments lasting an hour, during which he tried to find out more about the women, including their names, nationality and working hours.

He did not ask directly for sexual services but workers at all the salons offered them to him – either directly or indirectly –  at which point he terminated the appointment and left, the council said.

Amsterdam has been using undercover inspectors for three years to check for illegal prostitution. Officials closed eight massage salons at the end of 2015 where they suspected prostitution was taking place.