Cherie Blair has been hired by an erotic nightclub to challenge the smoking ban about to come into force in enclosed public places in England.
Mrs Blair is well known for her anti-smoking views
Dave West, who runs the HeyJo nightclub in London, believes the ban will breach the rights of staff and his guests.
Mr West told BBC Radio Five Live Mrs Blair was a "big champion of human rights" and she agreed with his stance.
Mrs Blair will be acting as his barrister under her professional name Cherie Booth QC.
The prime minister's wife, who famously made Mr Blair quit cigarettes as a condition of their marriage, said: "I think everyone well knows my views on smoking. But I keep to the rules of my profession."
Mrs Blair spoke as she marked the launch of Saturday's International Widows Day in London.
Mr West approached Matrix Chambers, where Cherie Booth is a founding member, to ask them to take on the case.
The smoking ban, which comes into force on 1 July, is one of her husband, Prime Minister Tony Blair's, flagship health policies.
But Mr West, who made his fortune from a discount alcohol and tobacco business in Calais, told BBC Radio Five Live: "What her husband is is one thing. She has a right to her own opinion to pursue her own job and that is to defend the working man."
After taking on the case Mrs Blair visited the £4m club in St James', central London, which 63-year-old Mr West describes as an "adult Alice in Wonderland".
Mr West fears the smoking ban, which will be introduced on 1 July, will force him to close it and his adjoining restaurant Abracadabra.
He told the Daily Mirror: "There is no room for manoeuvre when the ban comes in. I will be fined £2,500 each time it is breached.
"The only way for patrons to smoke after July 1 is by going out on the pavement and that could land me in trouble with the police if it creates noise or disturbance.
"I want to eyeball the authorities and am calling on other nightclubs to join me in the challenge."
A Matrix chambers spokeswoman said she took on the case under the "cab rank rule" - meaning it was the next available case and fell to her only by chance.
She added: "At the client's request she undertook a site visit, which was part of advising on the case."