Job Vacancy - Transport, industry and schools are set to be severely affected by the strike, the unions said. - Job Indonesia
The strike comes two days before the parliament in Lisbon is to vote on an austerity budget. - Lowongan Kerja
The budget aims to quell international unease over Portugal's public spending and deficit.
For the first time in 20 years, the country's main unions UGT and CGTP have united in a call for a national day of industrial action.
They expect workers from the private and public sector to take part in the strike, the head of the CGTP, Manuel Carvalho da Silva, said.
"The mobilisation of workers is enormous," he added.
The strike will hit banks, media and petrol supplies, the unions say.
They also aim to paralyse the country's ports, and hundreds of flights are set to be cancelled.
Many Portuguese have been angered by the government's plans to cut wages for public sector workers, freeze pensions and increase taxes.
Bond commitments However, analysts say the walkout is unlikely to stop the passage of the austerity budget, given that the opposition Social Democratic Party (PSD) has said that in order to not jeopardise the country's fragile finances it will abstain from the vote on Friday rather than vote against the measures.
The PSD position is crucial as Lisbon is trying to convince international investors that Portugal will not be forced to seek a bail-out like Ireland or Greece.
The austerity budget aims to reduce Portugal's deficit from 7.3% to 4.6% of GDP in 2011 through a combination of spending cuts and tax raises.
BBC Europe business correspondent Nigel Cassidy says that Portugal has failed to prosper or drive up productivity since joining the euro at what many now say was an unrealistic exchange rate.
The country found it especially difficult to compete with China in a previously strong sector, the manufacturing of textiles and shoes, our correspondent adds.
With 80% of its public debt held abroad, the country now finds itself at the mercy of bond traders and wants to convince the markets that it will be able to meet its commitments, our correspondent says.
Are you in Portugal? Will you be affected by the strike action?