By Nicolás Misculin

The action, which will hit sectors from transport to banks, is the biggest show of opposition to Milei's plans for spending cuts and privatization since he took office last month pledging to fix an economy reeling from 211% inflation and crippling debt.

The strike, coordinated by the powerful umbrella union the General Confederation of Labor (CGT), comes amid major scrutiny on Milei's two major reform pushes: his "omnibus" bill going through Congress and a "mega-decree" deregulating the economy.

The CGT had already used the courts to temporarily suspend some measures related to labor in Milei's decree.

The strike will start officially at noon (1500 GMT), but it was already affecting transportation, banks, hospitals and public services. Local airlines were forced to cancel hundreds of flights.

Milei, an economist and former TV pundit who pulled off a shock election win last year, is balancing stabilizing the South American country's economy and reducing a deep fiscal deficit with a painful cost of living crisis and poverty running at more than 40%.

"Milei wants a country where poverty and informal work reaches 90%," union member and national opposition deputy Hugo Yasky told local radio station Radio Con Vos.

"Now there is no job creation, what there is now is widespread misery, people's desperation, there are no measures to mitigate the damage they are causing."

Milei's government says the austerity measures are needed after years of over-spending that have left Argentina with huge debts to local and international creditors, including a shaky $44 billion deal with the International Monetary Fund (IMF).

"There is no strike that stops us, there is no threat that intimidates us," Milei's security minister and former presidential election rival Patricia Bullrich wrote on X.

"It's mafia unionists, poverty managers, complicit judges and corrupt politicians, all defending their privileges, resisting the change that society chose democratically."

(Reporting by Nicolas Misculin; Editing by Adam Jourdan and Alex Richardson)