Labour MP Geraint Davies has been suspended from the party after claims of “completely unacceptable behaviour”.
Labour said the allegations were “incredibly serious” and encouraged anyone with a complaint to report it to the party.
According to news website Politico, he is accused of subjecting younger colleagues to unwanted sexual attention.
The MP for Swansea West told Politico he did not recognise the allegations.
“None of them, as far as I know, has been lodged as complaints with the Labour Party or Parliament,” he said.
“If I have inadvertently caused offence to anyone, then I am naturally sorry as it is important that we share an environment of mutual and equal respect for all.”
The BBC has contacted Mr Davies for comment but has so far received no response.
Mr Davies has been administratively suspended from the party pending an investigation into the allegations.
This means he can not sit as a Labour MP while the investigation is ongoing, although he remains the member of Parliament for Swansea West and will sit as an independent.
Politico, which first reported the allegations, said it had spoken to more than 20 people who worked with Mr Davies in Parliament, including serving MPs and current and former Labour Party staff.
The new site said five women had claimed Mr Davies had subjected them to unwanted sexual attention, both physical and verbal.
The allegations, which go back at least five years, include excessive drinking, as well as sexual comments and unwanted touching of younger women, according to the website.
Some of the individuals said they had discussed his behaviour with Labour whips, who are in charge of party discipline.
Labour has not currently received any formal complaints about Mr Davies’s behaviour.
A Labour Party spokesperson said: “These are incredibly serious allegations of completely unacceptable behaviour.
“We strongly encourage anyone with a complaint to come forward to the Labour party’s investigation.
“Any complainant will have access to an independent support service who provide confidential and independent guidance and advice from external experts throughout the process.”
Mr Davies, who first became an MP in 1997, has sat on several Commons committees including the Welsh Affairs and Environment Committee.
Until 2005 he was the MP for Croydon Central and has also served as leader of the south London borough’s council.
In 2010 he became MP for Swansea West, where he currently has a majority of 8,116.
The allegations of inappropriate behaviour are the latest to emerge from Westminster, in what has been dubbed the “Pestminster scandal”.
Both Labour and Conservative MPs have faced accusations which have led to their suspension in recent years.
