Labour MP Dawn Butler tweeted last week about an incident in Westminster, where she was mistaken for a cleaner and told a lift she was using was not for cleaning staff.
But Steve Wilson, the husband of Penistone and Stocksbridge Liberal Democrat MP Angela Smith who also works as her office manager, replied to the tweet saying it was “just not true” and said accounts like Ms Butler’s “don’t do anyone justice and anyone propagating them should stop it”.
Mr Wilson has apologised for his tweet. He said: “I apologise for the offence I have caused. We must take responsibility for condemning racism and prejudice in all its forms, in order to stamp it out from our society.”
But Ms Butler, writing to Liberal Democrat leader Jo Swinson, said she “found the trolling deeply disturbing”.
She said: “To be accused of lying about a racist incident I experienced was particularly distressing. This type of gaslighting is totally unacceptable.”
Ms Butler added: “When I first entered Parliament I was told by another MP in a lift in Parliament that ‘this lift isn’t for cleaners’. He assumed I was a cleaner because I’m black. This isn’t a ‘story’ or a lie.
“This is race discrimination in the workplace; it is experienced by black, asian and ethnic minority people in workplaces across our country on a daily basis and we need to stamp it out.
“White men denying our lived experiences ad accusing those of us who do speak out about it of lying not only legitimises, but it actively promotes, racism.”
A Labour Party source said “the Lib Dems should immediately suspend him and fully investigate”. But added: “We won't hold our breath for them to take action."
Ms Smith came under criticism earlier this year for describing people from a black, asian or minority ehtnic background as having a “funny tinge" during an appearance on the BBC Two programme Politics Live.
Afterwards she apologised and said she had misspoken.
It was revealed last week that Ms Smith will not stand in Penistone and Stocksbridge in the next election.
The former Labour MP left the party in February to join Change UK but began sitting as an independent in June.
Now, under the Lib Dem banner, Ms Smith has announced she will leave her seat and instead challenge Conservative Sir Graham Brady in his Altrincham and Sale West seat, near Manchester.
Mr Wilson, who was a Sheffield councillor since 2011, also quit Labour in February. At the time he told The Yorkshire Post He told The Yorkshire Post: “I’ve had it up to here and I can no longer stay. I have come to the same conclusion as my wife.”