Liberal Democrat leader Nick Clegg has asked the party's chief whip to invoke disciplinary procedures against Portsmouth South MP Mike Hancock.The party confirmed Mr Hancock had received legal papers of a High Court civil action against him regarding an allegation of inappropriate conduct with a woman constituent in 2009.
Mr Hancock said he will "vigorously" defend himself against the claim.
The party said it was not pre-judging the case's outcome.
He is also accused of breaching the code of conduct at Portsmouth City Council, where he is also a councillor.
The party confirmed Mr Clegg has asked Chief Whip Alistair Carmichael to convene an urgent meeting under the disciplinary procedures of the parliamentary party between himself, Mr Hancock and deputy leader Simon Hughes.
Spy allegations A spokesman said: "Given the seriousness of the allegations, Nick Clegg has instructed the chief whip to invoke the disciplinary procedures of the party."
Mr Hancock, who said he will not attend the meeting due to medical appointments, said: "I have no intention of allowing any circumstances to bully me out of my job serving the people of Portsmouth.
"I will go at a time of my choosing or if the people decide to get rid of me."
Portsmouth City Council has not revealed details of the separate allegation against Mr Hancock.
The MP was arrested on suspicion of indecent assault in 2010 but never charged.
He was accused of "inappropriate behaviour", which he denied, towards a female constituent following a series of visits he made to her home.
It was alleged he placed his hand on her breast, exposing himself and kissing her without consent.
Mr Hancock hit the headlines in 2011 when he had an affair with his aide, Katia Zatuliveter, who was accused of being a Russian spy.
But the Special Immigration Appeals Commission said it had seen nothing to support the allegations against Miss Zatuliveter and she won an appeal against deportation.
Mr Hancock resigned from his post on the defence select committee as a result of the investigation but said he had not passed on material to Miss Zatuliveter that was not in the public domain or that was classified.
The councillor, who has been an MP since 1997, had major heart surgery last year after suffering from angina.