least once in their life, and 2.6% had done so during the past year. In practice According to the International Encyclopedia of Sexuality, during the 1990s, some 10% of prostitutes worked on the streets, 30% in window prostitution, 30% in sex clubs, 15% in an escort service, and 15% in their private residence. Drug addicts, including drug tourists, were said to be numerous in the street prostitution group. Some Dutch cities provide facilities called "afwerkplek", a sex drive-in enclosure for cars for street prostitution. According to Radio Netherlands in 2012, prostitution was concentrated in and around the big cities and in the border towns in the regions of Limburg, Groningen, Twente, West Brabant and Zeeland. Prostitution occurred in various forms: window and street prostitution, clubs, escort agencies, and home-based prostitution. Window prostitution occurred in 12 cities in the Netherlands. It was estimated that on average some 2,000 sex workers were engaged daily in this form of prostitution. Street prostitution existed in 10 Dutch cities and involved on average some 320 sex workers daily. Between 3,500 and 4,000 sex workers were employed daily in 600–700 clubs and private brothels. The extent of other forms of prostitution such as escort agencies and home-based prostitution was much more difficult to estimate. Home-based prostitution occurred in at least 17 municipalities, and escort agencies existed in at least 28 municipalities. In 2008, city statistic showed 142 licensed brothels in Amsterdam, with about 500 window displays, and officials estimated that sexual transactions in Amsterdam account for about 100 million US dollars per year. In 2011 Dutch authorities started asking sex workers to pay taxes on their earnings. Sex worker organisations National organisations Sex workers in the Netherlands have set up various organisations in order to guard their interests, including human rights, labour rights, healthcare and social inclusion. The first historical example of a Dutch labour union for sex workers was The Red Thread (De Rode Draad) (1985–2012). is a national sex trade union for (former) sex workers based in Amsterdam, founded in 2015 as a successor of The Red Thread. Red Light United was founded in 2019 as a trade union of (mostly migrant) window workers on De Wallen in Amsterdam. In addition, the / Soa AIDS Nederland is an Amsterdam-based organisation which runs a Sex Work Projects Programme to prevent HIV/AIDS and STIs amongst sex workers. International organisations Amsterdam is also home to several international