Ed Miliband has axed former leadership challenger Diane Abbott from her position in his frontbench team, according to reports.
The Hackney North and Stoke Newington MP said the Labour leader probably wanted "more message discipline", the BBC reports.
Neither Labour nor Ms Abbott's office would immediately confirm or deny the move.
Ms Abbott was the first black woman MP when she joined Parliament in 1987, and finished last in the 2010 contest which saw Mr Miliband chosen as leader.
She was appointed shadow public health minister in Mr Miliband's first frontbench team, but has since attracted attention after recently threatening to resign if the leader backed military action in Syria.
She has also hit the headlines for comments made on Twitter, including a post on the social networking site that said: "White people love playing divide and rule".
The BBC reported that Ms Abbott had confirmed her return to the backbenches, saying: “I think Ed wanted more message discipline. I'll live. These things happen.”
Ms Abbott is a prominent figure on Labour's left wing, and is often perceived as one of the most independent-minded MPs in the House of Commons.
In a speech earlier this year, she also expressed concern that the "pornification of culture" was creating a society where children were "hypersexualised" from a young age.
Her removal from the post comes a day after Mr Miliband demoted a set of leading Blairites, in a reshuffle which many consider a shifting of the shadow cabinet to the left whilst promoting women.
Mr Miliband moved Liam Byrne from work and pensions to be replaced by Rachel Reeves, leaving him responsible for higher education and with no seat at the top table.
Shadow defence secretary Jim Murphy was moved to oversee international development policy, with Vernon Coaker taking over his position, while Stephen Twigg has been ejected from education in favour of TV historian Tristram Hunt.
Additional reporting by Press Association