By Subir Bhaumik
BBC News, Calcutta
Police in the Indian state of West Bengal say Maoist rebels have attacked a showroom in protest over plans to build a factory to build small cars.
Protesters say that farmers have been forced to move
The protesters left behind posters after the attack - in central Calcutta - calling on the Tata company not to go ahead with the plans.
They argue that the new plant will displace scores of farmers.
Police say that similar attacks by Maoists have been reported from some other towns across the state.
"Leave Bengal and don't uproot our farmers," the Maoist posters said.
A committee of political parties opposing the Tata project called a 12-hour strike in the district of Hooghly on Monday, where the Singur plant is located.
The authorities say that order has now been restored
No violence has so far been reported.
In Calcutta, both the Trinamul Congress Party and the Bharatiya Janata Party (BJP) have publicly spoken out against the plant.
But West Bengal's Chief Minister, Buddhadev Bhattacharya, has said the Tata project will go ahead despite the opposition.
He said that work to fence the area earmarked for the plant - most of it cropland spreading over a 1,000 acres area - will be completed within the next two days.
Mr Bhattacharya is desperately trying to attract investment to rejuvenate the state's ailing economy.
"If this project cannot be implemented, we will lose out on many other projects that have been lined up for Bengal," he said.
"Most of the villagers have accepted our financial compensation and moved out of Singur. It is the outsiders like the Maoists and the Trinamuls who are behind the mayhem. We will not tolerate this," the chief minister said.
Trinamul Congress legislators in the state assembly walked out in protest over the chief minister's comments. But the chief minister said he was open to discussions with the opposition.
"I can talk to all parties with an open mind but I will not tolerate vandalism that will ruin our chances to get more investment once the Tata project is implemented," he said.
"There is no trouble in Singur now, everything is under control."
The Tata company plans to set up the factory to manufacture their proposed "People's Car", selling for around 100,000 Rupees (just over $2,000).
But opposition parties say that farmers have been "forcibly uprooted" to enable the project to go ahead. They argue that the plant should instead be built on fallow land.
Social activist Medha Patkar has joined the protests. On Monday, she was detained on her way to Singur - for the second time in less than a week.
On Saturday, scores of villagers led by the Maoists fought pitched battles with the police at Singur .
Police used teargas and baton-charges to break up the demonstration, and nearly 50 people were injured, including some women.