The taxman is homing in on Amsterdam's thriving sex industry, warning the city's prostitutes it is time they paid their share.

Prostitution has flourished in the city since the 1600s, when the Netherlands was a major naval power and sailors arrived at the port looking for a good time.

The country legalised the practice a decade ago, but it is only now getting around to looking at the sex workers who advertise themselves in shop windows in Amsterdam's red light district.

"We began at the larger places, the brothels, so now we're moving on to the window landlords and the ladies," said a spokeswoman for the country's tax service.

The move is meeting with little formal opposition, even among prostitutes - though some are sceptical it can be enforced. But it marks yet another shift away from the permissive attitudes that once prevailed in the Netherlands.

"It's a good thing that they're doing this," said Samantha, a statuesque blonde Dutchwoman in a white leather dress who offers her services from behind one of the hundreds of red-curtained windows in the heart of the city's ancient centre.

"It's a job like any other and we should pay taxes," she said.

She said she has been paying her share for years and felt she was competing on unequal terms with women who did not, many of them immigrants from Eastern Europe.

Although the Netherlands has weathered the fallout from the 2008 financial crisis better than many countries, the government ran a deficit of 6% in 2010 and is cutting spending and hiking taxes in hopes of balancing the budget by 2015.

Prostitutes were told they would be audited in typically bureaucratic fashion, with a notice addressed "to landlords and window prostitutes in Amsterdam" published last week in the city's main newspaper.

"Agents of the Tax Service will walk through various elements of your business administration with you, such as prices, staffing, agendas and calendars," the notice said.

"The facts will be used at a later date in reviewing your returns."

Although the Dutch state is not going to make a fortune just by squeezing prostitutes, the sex trade is a serious industry that went almost entirely untaxed until legalisation.

The Central Bureau of Statistics estimates prostitution generates £550 million a year.

Under Dutch law, prostitutes should be charging 19% sales tax on each transaction. Customers typically pay £40 for a 15 minute session. In addition, after-expense profits are personal income, taxed at anywhere from 33% for someone making less than £15,000 per year to 52% for people making more than £45,000.

Sex workers, who are almost all women, can fall beyond both ends of that range.

Nobody knows exactly how many prostitutes there are or how many of them pay tax, since legal ones are registered as one-women businesses, not brothels.

But a study in October estimated there are slightly fewer than 8,000 prostitutes of all kinds in the city, and 3,000 working behind windows. An industry think-tank called the SOR Institute believes around 40% of window prostitutes already pay some income tax.