As thousands of cash-strapped Italians take to the streets to protest against their tax bills, a small group of earners who have never paid a penny in tax are instead demanding their right to contribute to the nation's coffers.

Prostitutes up and down the country are fighting against a tax code that does not recognise their profession, even though paying for sex is legal, leaving them no chance to pay a cut of their earnings to the tax man and qualify for a pension.

"It is the height of hypocrisy that what I do is legal, but I cannot pay tax on it," said Efe Bal, 36, a Turkish transsexual prostitute who staged a naked protest in the rain outside the offices of Italian daily newspaper Corriere della Sera on Wednesday, delivering a tirade to two nervous-looking policemen as she barely covered herself with a full-page ad she had taken out in the paper the previous day.

Bal, a sex worker who has written a book called What Husbands Don't Say, has been plastering Milan, her hometown, with posters for months offering to pay tax.

What has really irked prostitutes is that, in a bureaucratic twist, the tax office has now decided to fine them for tax evasion, even though it has given them no way of paying tax.

Bal said she had decided to step up her protest after receiving fines worth €450,000 (£370,000). "It was calculated on payments into my bank account between 2008 and 2012 but didn't discriminate between earnings and the sale of property," she said.

Carol, 54, a Verona-based prostitute born in Ethiopia said she had been treated like an "extraterrestrial" and sent packing when she offered to pay taxes at her local tax office only to receive a bill for €70,000, based on a year's earnings. "That is an exaggeration since I work on the streets and earn €40,000," she said.

"I escaped the war in Ethiopia for a better life and now they are massacring me – I will never have a pension," she added.

Sandra Yara, a Brazilian former prostitute who is now married, said she had been surprised to receive a bill for €50,000 after being told by her local chamber of commerce that her work could not be categorised.

The prostitutes' campaign to pay tax is stepping up as around 60,000 shopkeepers and artisans descended on Rome's Piazza del Popolo this week to demand that the incoming government led by Matteo Renzi lower their tax burden.

To identify Italy's up to 70,000 prostitutes – half of whom are foreign born – tax police are scouring escort websites for names as they try to recoup desperately needed tax revenue, said Pia Covre, head of the Italian Committee for Civil Rights for Prostitutes.

"They have been trying to fit prostitutes into taxable categories and we have heard of women being told they have been classified as working for marriage agencies," said Covre.

Bal, who speaks four languages, said she had done well from her trade, earning up to €20,000 a month before the current economic crisis halved her income. Transsexual prostitutes are a common sight on Italian streets, a phenomenon Bal put down to "widespread bisexuality" among customers.

Bal proposed a scalable tax structure for prostitutes which would estimate their income based on their age and ask them to pay less as they get older.

"Nobody said anything about this issue until I showed my bottom," she said. "My dream now is to visit the head of the Italian tax office and tell him 'I am a prostitute and I want to pay my taxes'."