Huge crowds gathered outside parliament in the heart of Buenos Aires for one of the biggest demonstrations in recent years, heeding the strike called by the South American country's main labor union, the CGT, France 24 reports.
Protesters bore placards reading "The homeland is not for sale" and "Eating is not a privilege" as they marched to the beat of drums and sound of exploding firecrackers and held aloft a giant effigy of Milei.
"We come to defend 40 years of democracy, defend the homeland," CGT leader Hector Daer told the crowd.
"Walking around with a chainsaw is one thing, governing is another," he added in reference to Milei's frequent brandishing of a chainsaw on the campaign trail as a symbol of his envisaged public spending cuts.
Ten days after he came to power in December, the new president announced a set of sweeping reforms that lessened some worker protections, abolished a price ceiling on rent and lifted price controls on certain consumer goods, among other things.
Poverty levels in Latin America's third-biggest economy are at 40 percent and the country is battling annual inflation exceeding 200 percent after decades of financial mismanagement.
The main rally in the capital targeted Parliament, where lawmakers are discussing Milei's package of deregulation and economic reform, which many citizens fear will leave them vulnerable to exploitation, and poorer.
Some 80,000 gathered in Buenos Aires, according to the police, while protesters put the number at half-a-million.
Demonstrations were also held in numerous other cities and towns, gathering thousands more.
The CGT was joined in its call for action by smaller unions and civic groups, vowing to "not yield an inch of what has been achieved" in terms of worker and consumer protections, according to another CGT leader Pablo Moyano.
Air traffic was affected early by the strike, with Aerolineas Argentinas cancelling nearly 300 flights "affecting more than 20,000 passengers" for a loss of about $2.5 million, according to the company.
