Ms Rees, who has represented Neath since 2015, loses whip pending an investigation.
Neath MP Christina Rees has been suspended from Labour following reported allegations of bullying.
The politician, who has represented the constituency since 2015, has lost the party whip pending an investigation.
It means the former shadow Welsh secretary will sit in the Commons as an independent. The Guardian said Ms Rees faces allegations of bullying staff.
Ms Rees told the newspaper she was cooperating fully with the investigation.
The Guardian reported the move followed complaints by staff working for her in her south Wales constituency. Labour has declined to comment.
The MP took her seat in 2015 after Peter Hain stood down at that year’s general election.
She is the 14th MP to be sitting in parliament as an independent, joining others who have lost the whip from their parties.
Born in the village of Kenfig Hill in south Wales, the qualified barrister has represented Wales in squash more than 100 times.
She was a member of the Great Britain Youth Team to the Munich Olympics.
Ms Rees, who served on the Labour frontbench during Jeremy Corbyn’s leadership, was married to former Welsh Secretary Ron Davies until they divorced in 1999.
She told the Guardian: “There has been a complaint made against me to the Labour Party, which is under investigation and I am therefore under an administrative suspension until the process is concluded. I’m not aware of the details of the complaint but I am fully cooperating with the investigation.”