Sarkozy, who was defeated in last year's elections by President Francois Hollande, posted on his Facebook profile on Friday that a decision by France's Constitutional Council "threatens the political party that must prepare the necessary alternative to socialism."

The 58-year-old ex-leader was referring to Thursday's decision by the Constitutional Council decision to uphold an auditor's previous ruling that his right-wing Union for a Popular Movement (UMP) party would not be reimbursed 11 million euros ($14 million) from Sarkozy's 2012 reelection campaign because the party had gone over campaign spending limits.

Normally, a party is entitled to a 47.5 percent reimbursement of campaign expenses, but the UMP exceeded the limit by 2.1 percent.

Sarkozy was a member of the Constitutional Council, which is France's top constitutional body, but the body's decision prompted his resignation on Thursday.

"I have to take on my responsibilities by committing myself to guaranteeing the freedom of democratic expression in our country," Sarkozy said on Facebook. "I ask you to help me by mobilizing, as I will, to this end."

He also attached a link to his party's website for donations.

The right-wing newspaper Le Figaro said the council's decision had dealt a "hard blow" to Sarkozy's party and "threatens to exacerbate the UMP's already very-difficult financial situation."

Comeback?

According to UMP party sources interviewed by the AFP news agency, Sarkozy is planning to attend an extraordinary meeting with UMP leaders on Monday.

Sarkozy is rumored to be considering a return to politics, with France's next presidential election due in 2017.

The UMP has been struggling since Sarkozy's defeat, with party leader Jean-Francois Cope and ex-prime minister Francois Fillon embroiled in a bitter public leadership battle that has hurt its reputation.

Sarkozy has stayed out of the political spotlight since his loss of the presidency. Instead, he has resumed his corporate law practice and lectured on the international circuit.

mz/ipj (AFP, dpa)