A key bloc within Syria's main opposition National Coalition announced its withdrawal from the body on Monday, accusing some leaders of misusing funds and being motivated by personal ambition.
The Syrian Revolution General Commission said in a statement: "We are withdrawing from the Coalition... because it is taking initiatives far removed from the true revolution and cannot represent the revolution in an authentic way."
A member of the National Coalition since its creation, the SRGC is one of the longest-established organisations on the ground backing the rebellion against President Bashar al-Assad.
It comprises a network of activists across Syria that is linked to armed rebels fighting Assad's forces.
"Coalition members are more interested in appearing in the media than helping the revolution," the SRGC statement read.
"A lot of money has been wasted because they used it for their own personal interests while the Syrian people inside the country lack everything."
The SRGC went on to add that during the last meeting of the Coalition, which finished late Thursday in Istanbul, "the agreement that rebels on the ground would have one third of the seats was not respected when the membership was expanded."
George Sabra, interim head of the Coalition, announced at the end of the meeting that 51 new members had been admitted to the body, bringing the number of representatives to 114, of whom 15 are from the rebel Free Syrian Army.
The SRGC accused "some countries of manipulating the revolution for their own ends and trampling the blood of our people".
"Each of these countries puts their blocs up against the others, and these blocs act in line with agendas foreign to the revolution," it said.
The Coalition's expansion came amid what opponents have described as intense regional and international pressure, led by powerhouse Saudi Arabia, which seeks to offset the grip over the group of Qatar and the influential Muslim Brotherhood.