Margaret Ritchie is to be challenged for the leadership of the SDLP.
Deputy leader Patsy McGlone said he will stand for election at the party's annual general meeting in November.
Even though South Down MP Ms Ritchie only took over at the beginning of last year, Mr McGlone said it is time for change at the top.
The move follows a poor performance by the party in Assembly elections earlier this year
Ms Ritchie is the first leader to face a challenge since the party was founded in 1970 and Mr McGlone, a Stormont MLA from Cookstown, Co Tyrone, is likely to have the backing of several key members.
He said: "The SDLP has revolutionised Irish politics. The founding principles of the party are as relevant today as they were during the civil rights campaign.
"The unity of the people of Ireland, a unity built on trust, along with practical social democracy - being there for people through the good and bad times - lie at the heart of every SDLP member and supporter.
"The way forward for us needs three strategic elements: strong leadership, clarity of message and radically improved grassroots organisation.
"The SDLP has a wealth of talent within its ranks, and each member has a vital role to play in contributing to the community as we strengthen our grassroots base. Now, as over the last 40 years, we are here as the strong voice of integrity in politics."