Hundreds of workers shout anti-government slogans and waved flags in noisy protests outside airports in the cities of New Delhi, Bombay, Calcutta and Bangalore.
Policemen in riot gear were deployed at all major airports.
In Bombay, the protests turned violent as police used canes to disperse demonstrators trying to enter an airport building.
The workers demand that the government scrap plans to hand over the Delhi and Bombay airports to two consortiums for modernization. They fear the plans will jeopardize their jobs.
The revamp of the rundown airports has been long overdue. Both are struggling with booming air traffic, and are running out of runways and space to handle the increased flight load that has accompanied India's economic growth.
The employees say they do not oppose plans to upgrade the airports, but say the government, which currently runs these airports, should do the work.
The strikers are supported by leftist parties that lend crucial support to the government. Brinda Karat, a senior leader of the Communist Party of India (Marxist) says the government is equipped to undertake the revamp on its own.
Karat says leftist parties will not compromise on the issue, and accuses the government of putting the interests of private companies over national interests.
The government wants to have private companies pay the billions of dollars in renovation costs, and then recover their investment by operating the facilities.
Civil Aviation Minister Praful Patel said Wednesday the government is pressing ahead with its plans.
Mr. Patel says the cabinet has approved the bids of two private groups for modernization of the New Delhi and Bombay airports.
The contract for the New Delhi airport is being given to India's GMR group, which is collaborating with German airport operator Fraport. The Bombay airport will be given to India's GVK Industries and the Airports Company of South Africa.
The role of foreign companies in the privatization also angers the leftist parties, which do not want to see national assets in foreign hands.
The government has sought to allay worker fears, saying all employees will be retained for at least three years after the companies take over the airport operations.
Despite the strike, most airports functioned normally. Officials say there was no disruption of flights because air traffic controllers have not joined the protests.