The Conservatives have removed the whip from senior MP Julian Knight after a complaint was made to the Metropolitan Police.
Chief Whip Simon Hart removed the Tory whip, meaning Mr Knight no longer sits in the Commons as a Conservative, after the complaint was made on Wednesday evening.
Mr Knight is the chairman of the Commons Digital, Culture, Media and Sport Committee.
The 50-year-old has represented Solihull in the West Midlands since 2015.
A spokeswoman for Mr Hart, the government's Chief Whip, said: "Following a complaint made to the Metropolitan Police this evening, we have removed the whip from Julian Knight MP with immediate effect."
She declined to comment on the nature of the complaint now it is under investigation.
The Metropolitan Police also declined to comment.
Also on Wednesday night, Labour MP Conor McGinn was suspended from the party pending an investigation.
Mr McGinn, who has represented the St Helens North constituency since 2015, will now sit as an independent MP.
Details of the nature of the inquiry have not yet been confirmed.
In a statement given to The Guardian, Mr McGinn said "I strongly reject any suggestion of wrongdoing and I look forward to the matter being resolved quickly.
"I have not been told the details of the complaint but I am confident that it is entirely unfounded.
"The Labour party has informed me that it is automatically required to apply a temporary procedural suspension while a complaint is investigated."