Charities working with refugees and migrants in the camp in Calais are objecting to the government's plan to dismantle the camp and disperse the occupants.
Although no date has been announced for the closure of the slum-like camp, known as the Jungle, the French government has announced it will happen by the end of the year.
The first group of migrants is expected to be moved as soon as next week.
Ahead of a meeting at France's Interior Ministry, homelessness charity Emmaus asked for postponing the closure because it says "all conditions are not met for an efficient humanitarian operation to take place".
A church organisation, Secours Catholique, says it is also opposed to cleaning up the area, where up to 10,000 migrants are living in squalid conditions.
"The government is heading straight into a wall," said Thierry Kuhn, president of Emmaus France.
"We should not bury our heads in the sand; people will come back as long as we won't be able to offer them a solution adapted to their life plan."
The government announced plans in the summer to disperse Calais migrants to centres across France, where they will be able to apply for asylum.
Emmaus says a large proportion of migrants in the camp who fled from countries such as Syria, Iraq and Afghanistan have no interest in staying in France, but hope to cross the English Channel to Britain.
"The government says that people in Calais are seeking asylum, but they have no idea many want to reach the UK," Emmaus official Frederic Amiel told The Associated Press.
"The government needs to take its time, otherwise half of the people in the Jungle won't find a place in the relocation process. They will disperse and return."
The head of Secours Catholique in the Calais area, Vincent de Coninck, is also adamant the port city will remain a transit point to Britain.
"Exiled people will return tomorrow," he said. "That's the reason why it seems dangerous to us to destroy the day centre and its showers, its women's house as well as the temporary shelter offering 1,500 places."
Earlier this month, the head of the government's human rights watchdog, Jacques Toubon, also expressed concerns about the planned demolition.
Mr Toubon said in a statement that dismantling the slum "will further weaken vulnerable people's lives and drive them away from the protection they are entitled to by their fundamental rights".