Three Tory MPs have lodged a complaint against party colleague Lord Sheikh over his attendance at a conference on Palestinian rights in Tunisia in 2014.
Lord Sheikh confirmed he was at the event, as Labour’s Jeremy Corbyn faced questions about his participation in a memorial ceremony during the same trip.
The Conservative Muslim Forum founder said he did not attend the controversial wreath-laying ceremony.
But MPs Zac Goldsmith, Robert Halfon and Andrew Percy want an investigation.
The International Conference on Monitoring the Palestinian Political and Legal Situation in the Light of Israeli Aggression took place in 2014.
It has been in the headlines since photographs emerged showing Mr Corbyn at a wreath-laying ceremony, close to the graves of people accused of links to the 1972 Munich Olympics attack in which 11 hostages from the Israeli team and a West German policeman were killed.
The Labour leader has said he attended the event to remember victims of a 1985 Israeli air strike on Palestinian Liberation Organisation offices in Tunis.
Lord Sheikh said he knew nothing about the wreath-laying and did not go to it. In a statement, he said he had been invited to the conference by the President of Tunisia.
“The meeting was held in the context of the Arab Spring which affected the whole of the Middle East and North Africa,” he said.
Lord Sheikh said he had “very balanced” views on Palestine, saying he was against any form of anti-Semitism and highlighting examples of joint working with Jewish peers.
But in a letter to the Conservative Party board, Mr Goldsmith and Mr Halfon said it had been “no ordinary conference”, adding that “evidence suggests this conference was addressed by anti-Semites and terrorists”.
They said the Conservatives could not criticise Mr Corbyn over the event while allowing a Tory peer’s attendance to pass “without comment or complaint”.
“In our opinion, Lord Sheikh’s attendance at this conference was hugely disappointing and raises significant questions that need to be answered,” they wrote.
Mr Percy told the BBC he had made a separate complaint.