Many forest tracks – which are usually frozen solid at this time of the year – have been inaccessible to logging trucks because the ground was too soft, fine paper maker M-real said.
Forestry is a key industry for the Nordic country, making some 20 percent of its total exports. December was 6-8 degrees warmer than usual in Finland and the warmest since records began, the Finnish meteorological institute said.
But a thaw in a country renowned for its harsh winters has been playing havoc with supplies, M-real said.
"The company is living from hand to mouth with its wood supply. Possibly we have to limit our (paper) production if the weather does not get colder," said Juha Mantyla, M-real's director for wood sourcing.
There were signs on Friday of a return to more normal weather with temperatures dipping below freezing in the capital Helsinki.
Global warming, stoked by greenhouse gases from burning fossil fuels, and an El Nino warming of the Pacific Ocean are widely blamed by scientists for mild weather in Europe, at the start of what scientists say may be the warmest year on record.
The United Nations says 2006 was the sixth warmest year worldwide since records began in the 1860s. US government forecasters say 2006 was the warmest in the United States since records began there 112 years ago.
M-real had already cut production at its saw mills due to lack of wood, Mantyla said.
"We have some timber stored by roadside, and will be able to pick those up after one good, cold day, but we would need temperatures of about -10 (Celsius) for three days to be able to cut timber on soft ground," Mantyla said.
Of M-Real's total production, 36 percent comes from Finland. It also uses imported wood from Russia and Baltic countries, where warm weather has also hurt logging.
M-real's bigger rivals -- the world's top paper and board maker Stora Enso and the largest magazine paper maker UPM-Kymmene -- said they were more positive about Finnish wood supply.
"We can manage January without disturbances to production on paper and pulp mills, and in saw mills," said Sixten Sunabacka, head of wood sourcing at UPM. He said the company has already cut back its Finnish plywood production.
Stora Enso's wood sourcing head Matti Karjula said the firm was receiving enough wood to keep production running.