Ken Livingstone has been suspended by the Labour Party over comments he made while defending an MP at the centre of an anti-Semitism row.
The ex-London mayor will be investigated for "bringing the party into disrepute".
Labour MP John Mann, who accused Mr Livingstone of being a "Nazi apologist" in a confrontation outside a BBC studio, faces a reprimand.
Mr Mann had been referring to comments Mr Livingstone made about Adolf Hitler.
"The Chief Whip has summoned John Mann MP to discuss his conduct," Labour said in a statement.
The row was prompted by the suspension of Labour MP Naz Shah over comments she made about Israel on social media.
Politics Live: Labour and anti-Semitism row
Labour criticism of Mr Livingstone mounted when he appeared on BBC Radio London defending Naz Shah - and said he had never heard anyone in the Labour Party say anything anti-Semitic.