Robbie Williams and his wife Ayda Field have strongly denied claims that she sexually harassed their personal assistant.
The couple has pledged to "strenuously" defend themselves after the "disgruntled" former employee took legal action against them.
Gilles De Bonfilhs is suing Mr Williams over claims that his wife, an American actress, sexually harassed him before he was fired, according to the US news website TMZ.
A spokesman for the 41-year-old former Take That star said the claims were "entirely without substance".
"The claims [are] being made by a disgruntled former employee, after he was sacked for serious misconduct," he said.
"Any proceedings will be strenuously defended. There will be no further comment on the matter as it is in the hands of the lawyers."
It is understood that Mr De Bonfilhs stopped working for the British singer and his wife in January.
Mr Williams is said to be listed in court documents as a defendant, though De Bonfilhs makes no sexual harassment allegations against the star.
According to reports, his lawsuit claims Ms Field "walked around in various stages of undress, shared details about her sex life, questioned him about his sex life and asked him to answer questions and comment on her body".
The couple began a relationship in 2006 and married in the grounds of Mr Williams' Beverly Hills mansion four years later.
They have two children, two-year-old Theodora Rose and Charlton Valentine, who was born in late October 2014.
In an interview last October, Mr Williams revealed how he had sought to cast off his bad boy image.
"I love my wife's company. She gives me a lot of energy - she's like a one-woman cheerleading team," he said.
"Touring is mostly about waiting, being bored. When you're bored you get lonely, but fortunately I don't have to be because my best friend is with me. We get on very well and she keeps me entertained.
"She has anchored my life and made me feel secure, and saved me from a life of self-destruction."
He added: "I'm a fiercely self-absorbed narcissistic person, and my daughter being on tour with me means I'm forced to think about someone else." (© Daily Telegraph London)