"The majority of non-governmental organisations (NGOs) will have to suspend their activities on October 18," said Yury Dzhibladze, head of the Centre for the Development of Democracy and Human Rights in Moscow.
Out of an estimated 200 to 500 foreign non-governmental groups operating in Russia only around 80 have been registered and papers for 72 others are still being examined, registration officials said. All the rest face suspension.
While officials say in private they will be tolerant towards organisations that do not manage to register in time, many campaigners fear suspension will seriously disrupt operations.
Organisations that could be affected include charities that have helped prop up Russia's faulty social welfare system in the years following the collapse of the Soviet Union, as well as adoption agencies and human rights groups.
"Very few human rights organisations have submitted their papers to our service," Sergei Movchan, director of the federal registration service, said at a news conference on Monday.
"Some of them want to build up an image as victims of repression in Russia," said Movchan, whose government agency is in charge of registering foreign non-governmental organisations.
The law, which came into force on April 17, obliges NGOs to re-register with Russian authorities and requires them to submit regular reports on their activities and sources of finance.
Groups not registered before Wednesday will no longer be allowed to operate in Russia but have been granted the right to submit papers after the deadline and await registration.
Several campaigners have complained that the new law will make it more difficult to obtain financial help from abroad and will give the authorities an excuse to shut down organisations seen as too critical of the authorities.
One of the groups affected will be Amnesty International, which only submitted registration papers on Monday, although the organisation blamed red tape for the delay. The registration procedure takes around a month.
But the situation is far less critical than civil society campaigners had originally thought and several have welcomed steps taken by Russian authorities to make the process easier.
"We were sure that foreign unregistered NGOs were going to be forced to close their offices and leave the country," Dzhibladze said.
"But the authorities have agreed to just suspend their professional activities until registration," he added.
An official from the registration service, Anatoly Panchenko, said: "The federal registration service will not shut down unregistered NGOs, they will continue to exist as juridical entities and their employees will continue to be paid."
So far, three foreign NGOs have been denied registration and several have been asked to re-submit their papers, officials said.
Starting October 31, NGOs will also have to send a report on their financial activities and their programme for 2007. "If the report does not correspond to the aims proclaimed in official documents, we will have the right to close the NGOs," Movchan said.

Copyright AFP (Agence France-Presse), 2006