Normal life has been disrupted in the city
The operators of private buses and taxis in India's third most populous city, Calcutta, have begun an indefinite strike.
The action is in protest against a decision by the West Bengal government to implement a ban on commercial vehicles more than 15 years old.
The ban, ordered by Calcutta's high court, aims to cut pollution.
A study found that 70% of Calcutta's 18 million residents suffer from breathing problems or respiratory disease.
The ban will be effective from 1 August. But with some 60,000 taxis and 10,000 buses currently standing idle, the strike is having a major impact, correspondents say.
There are huge crowds at metro stations and schools and universities are shut.
Dilip Chakrabarty, a physiotherapist, said he was stuck because of lack of transport.
"I am not attached to a hospital, so I go to patients at home. Today, I am stuck because I can't find buses quickly enough. So I will attend to less than half the patients I normally handle."
The state transport minister Subhas Chakrabarty has said that efforts to prevent the strike failed because the transport operators were unreasonable.
"I wanted the issue to be amicably settled. But they insist on going ahead with the strike, so we will take very tough action," Mr Chakrabarty said.
The city's ageing vehicles are seen as one important cause of air pollution and responsible for the sharp rise in lung cancer and similar diseases in the city.
Mr Chakrabarty said that nearly 3000 buses and mini-buses and almost 6500 taxis will have to go off the roads or convert to green fuel because they were bought more than 15 years ago.
Operators say they would have no hesitation in switching to green fuels or buying new vehicles but they say they need soft loans and easy repayment terms to help them make the switch.
Nearly 3000 old buses are planned to be scrapped
"We understand the environmental concerns, the need to protect our people from pollution. But most of us don't have enough money to buy new taxis and buses on our own and the banks are cautious to lend in a climate of economic downturn," said Swarnakamal Saha, chief of the bus operators association.
"This is where we want government support."
But environmentalist Subhas Dutta, who filed the case in the high court that led to the judgement, says that transport owners have had enough time to organise funds and switch to new, green-fuel vehicles.
"This case has been in the court for a long time and the transport associations tried their best to stop an order for scrapping of old vehicles. Now they have no excuse," Mr Dutta said.