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It's only breakfast time in Paris, but Jean Lassalle's mobile phone keeps vibrating on his desk.

"It's a good omen. A lot of mayors are calling me," the 61-year-old centrist lawmaker said.

A stone's throw from the Eiffel tower, excitement is building up at the presidential hopeful's headquarters. Lassalle's small campaign team is trying to secure the final endorsements he needs to be a presidential candidate, and his aides are busy working the phone.

"I've got the Murols mayor on the line, he wants to endorse your bid," campaign communication director Celine Alleaume said as she rushes into Lassalle's small office.

With just a few days left to capture the required backing to run for France's president, it's now or never for the lesser-known candidates.

Under French law, bidders need to receive the political backing of 500 mayors, or elected officials, to be allowed to run for president. First introduced in 1962 under Charles De Gaulle when France implemented direct universal suffrage for the presidential election, the law was meant to eliminate fringe bids.

Only 100 endorsements were initially required but the large numbers of candidates in the 1965, 1969 and 1974 elections led to stricter screening.

The system did not, however, prevent largely-unknown rightist Francois Asselineau from securing the necessary endorsements. Meanwhile, far-left candidate Phillipe Poutou, whose NPA party is well established on the French political stage, fears he won't make the cut before Friday's deadline.

Many believe the law is flawed.

"This law is undemocratic. It could prevent the only working class candidate from bidding for president," said Poutou, an employee at a Ford factory who qualified for the 2012 election but has collected only 245 endorsements so far.

Lassalle, who made headlines back in 2006 when he lost 21 kilograms during a hunger strike for preserving jobs in his constituency, claims the system has been perverted over the years.

"Officials are worried they will be disliked by voters because of their endorsement, they fear they will end up looking like traitors," Lassalle said in an interview with The Associated Press on Monday.

As of Monday, the Lassalle team said he had collected 450 endorsements.

It's still a long way to go for Poutou, who admits he might have started the race a bit late.

"But it's been eight or nine months already," he said. "We have been sending comrades on the roads, some of us had to use their paid leave. We have been in contact with about 10,000 elected officials," he said.

For Poutou, the system is rigged because it favors big political machines which can apply strong pressure on local representatives obeying orders for fear of reprisals. He says for instance that the Socialist and Communist parties have issued guidelines for their elected officials across France preventing them from backing candidates other than Benoit Hamon or Jean-Luc Melenchon.

Hamon won the Socialist primary while Melenchon is backed by the Communist party. Both are among a group of eight candidates who have secured the 500 endorsements that also includes far-right politician Marine Le Pen, independent centrist Emmanuel Macron and conservative hopeful Francois Fillon.

Another issue for Poutou is the amendment to the law voted last year, which stipulates that all endorsements should now be made public, with backers' names published twice a week by the Constitutional Council, France's highest court.

"It makes things even harder," the 49-year-old Poutou said, arguing that many mayors he spoke with were reluctant to back his bid because of the small numbers of signatures he managed to gather so far.

"Given the strong pressure on us, they think: 'Why should we take the risk of supporting someone who is not even guaranteed to qualify?" Poutou said.

Charlotte Marchandise, who is campaigning without the support of a big political organization after she won an online primary, has only a few hopes left — despite the 32,685 votes she received on the Internet.

Like Poutou, Marchandise supports the introduction of a new system that would allow candidates to run if they gather a large amount of signatures from French citizens.

"A number as high as 500,000 could be a good solution," she said. "The way the system currently works, with the pressure on elected officials, is undemocratic. A mayor told me that after he endorsed my bid, his town dropped in the list of places due to be equipped with the optic fiber. It's like a mafia system."