Labour leader Sir Keir Starmer is being investigated by the Parliamentary Commissioner for Standards over potential breaches of rules on earnings and gifts, the parliamentary website shows.
According to the body's website, the MP for Holborn and St Pancras is being probed under two sections of the MPs' rules of conduct on registering interests.
The first matter under investigation is stated as: "Registration of interests under Category 1 of the Guide to the Rules (Employment and earnings)."