The oldest profession in the world is pitting its girl power against one of the richest.

A foundation representing prostitutes in the Netherlands has filed a complaint against Dutch financial giant ING, because the bank does not allow them to open business accounts.

Rode Draad (Red Thread), as the foundation is known, maintains that ING and other Dutch banks fail to treat prostitution - which is legal in the Netherlands - as a proper profession.

In an attempt to open up access for prostitutes to financial services, Rode Draad has filed a complaint with the Netherlands' Office of Fair Treatment, which deals with inequality issues.

"[ING] has refused to allow them business accounts and this is not equal treatment," Christie ten Broeke, a member of Rode Draad's board, told BBC News Online.

"Because most prostitutes are women, we have used this to make a complaint," she added, explaining that the Office of Fair Treatment only deals with issues such as race or gender.

ING defends itself by saying that it has a policy of not doing business with the sex industry.

"It's not a moral judgement," Peter Jong, a spokesman for the bank, said.

"Our decision is pure business. It is too big a risk. The sex industry is not stable or transparent and it is difficult to calculate risk."

Prostitution was legalised in the Netherlands in 1815 under the French emperor Napoleon, who was governing the territory at the time.

In 1988 it was defined as a legal profession and prostitutes were permitted to join a trade union.

However, 13 years on prostitutes still have problems getting home insurance, mortgages, or indeed any financial service that requires them to state their occupation.

And yet, as self-employed professionals, prostitutes are required by law to pay income tax and contributions to a Dutch disability insurance fund.

Currently, prostitutes face little difficulty opening private bank accounts - although ING has only recently allowed this - because they are not required to reveal their line of work.

However, opening a business account is preferable as it presents certain tax advantages.

Prostitutes who can show that they earn business income can reclaim tax on expenses such as condoms and sex toys.

Being treated as a commercial customer also makes it easier for prostitutes to take out loans to improve their businesses.

Rode Draad, which represents about 20,000 prostitutes, filed its complaint - based on individual complaints from prostitutes - earlier this year.

Last week, representatives of the foundation, including Ms ten Broeke, attended a meeting at the Office for Fair Treatment with ING to discuss the issue.

"We met with an [ING] lawyer and another man whose function was not made obvious to us," Ms ten Broeke said, obviously irritated that the bank had chosen not to send any senior officials.

During the hearing, ING defended its actions by saying that the sex industry was not transparent enough and that financial relationships with prostitutes could make it vulnerable to money laundering.

But Ms ten Broeke responded that any prostitute paying in large amounts of dirty money would immediately arouse suspicion.

"The tax people would be on them like ticks and fleas," she said.

ING is also concerned that dealings with prostitutes would not go down well with its other clients in countries that are "not as liberal as the Netherlands", said Mr Jong.

The Netherlands' other banking giant, ABN Amro, claims not to be so squeamish.

Geert Pielage, a spokesman for ABN Amro, told BBC News Online, "We don't exclude a group in advance."

The key issue is whether their activity is legal or illegal, he added.

"A prostitute is treated like a normal client, just a business woman.

"If she wants a financial relationship with us, we look over her business," he said, though he  noted that the bank did not accept every application.

In Ms ten Broeke's view, however, Dutch banks are generally not so accommodating.

"Many institutions don't give [prostitutes] professional recognition," she said.

The Office of Fair Treatment is due to make a decision on the case in a matter of weeks - by 24 September at the latest.

Although the Office cannot force ING to open up business accounts to prostitutes, its ruling would be influential and could set a precedent.

ING's Mr Jong concedes that the bank might have to revise its policy, if the ruling goes against it.

"It's hard to say if we would change our policy.

"There are a lot of famous judges and lawyers working at the [Office of Fair Treatment].
"It's not something we can do nothing about [if we lose the case], we would want to discuss it very thoroughly."

Such sentiments will no doubt cheer the Rode Draad camp, which is keen to forge a milestone on the road to commercial recognition for prostitutes.

And besides, whether the foundation wins its case or not, the publicity has been great, admitted Ms ten Broeke.

"We have had a little publicity to show what a totally ridiculous concept this is," she said.