Labour says the decision to expel Alastair Campbell from the party after he voted for the Liberal Democrats will be reviewed.
Shadow attorney general Shami Chakrabarti said parties have "automatic rules" for people who vote for other parties, but added that Mr Campbell, a former spokesman for Labour former prime minister Tony Blair, could be allowed back.
Mr Campbell was expelled from Labour after it emerged he voted for the Lib Dems in the European elections.
Speaking on BBC Radio 4's Today programme, Baroness Chakrabarti said: "Now there will be a review, which is appropriate.
"I don't want to cut across this review, I'm not part of that process. I would not like to see this drag on.
"Political parties have rules about people who support other parties, but I hope this case will be reviewed."
Baroness Chakrabarti said many people had decided not to vote for Labour for "heartfelt reasons" and this should not be grounds for expulsion. She said she hoped the review could be conducted quickly.
The decision to expel Mr Campbell has been unpopular with some in the Labour Party, with deputy leader Tom Watson branding the move "spiteful".
Mr Watson called for an "amnesty" for members who did not support the party at the European elections.
He said: "It is very clear that many thousands of Labour Party members voted for other parties last week. They were disappointed with the position on Brexit that a small number of people on the NEC (National Executive Committee) inserted into our manifesto.
"They were sending the NEC a message that our position lacked clarity and they were right.
"It is spiteful to resort to expulsions when the NEC should be listening to members.
"The politics of intolerance holds no future for the Labour Party. A broad-church party requires pluralism and tolerance to survive.
"There should be an amnesty for members who voted a different way last week. We should be listening to members rather than punishing them."