Air traffic controllers were the first to go on strike, grounding flights in and out of PortugalA 24-hour strike in Portugal has grounded flights and halted public transportation in protest against proposed austerity measures.
Air traffic controllers and workers on Lisbon's metro system were the first to go on strike late on Wednesday.
They are expected to be joined by hundreds of thousands of other workers, including teachers and hospital staff.
Parliament votes next week on a deficit reduction plan imposed as a result of an EU and IMF bailout.
The strike is expected to one of the biggest in Portugal's history, where mass industrial action is rare.
The strike is being supported by the two main labour unions, which represent more than a million workers.
Many Portuguese are shocked by the scale of austerity the budget implies, says the BBC's Alison Roberts in Lisbon.
The government proposes spending cuts across a broad range of public services, including health care and the armed forces, and tax hikes.
Also planned is the elimination of Christmas and holiday bonuses equal to about a month's pay for most public sector workers and allowing private firms to extend the work day by 30 minutes without overtime pay.
Under the terms of its 78bn euros ($105bn; £67bn) bailout, Portugal's government must sharply reduce its deficit.
With the unemployment rate higher than 12% and the economy forecast to contract next year, the conservative government of Prime Minister Pedro Passos Coelho has said there is no choice but to slash government spending.
"It is up to me to try to mobilise the Portuguese for action every day to contribute to transform Portugal," he said.
Mr Coelho became prime minister in June after the socialist government collapsed over the budget cuts. His governing coalition has a majority in parliament so the final vote next week on the 2012 budget is expected to pass.
Portugal was the third country after Greece and the Irish Republic to receive a bailout. Further instalments of the emergency loans could be withheld if it does not meet targets for deficit reduction.
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