BUENOS AIRES (Reuters) - Argentine truck drivers paralyzed parts of Buenos Aires, throwing up road blocks in some of the city’s busiest downtown neighborhoods, in a protest on Wednesday against President Mauricio Macri’s market-friendly economic policies.

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The protest was seen as a test of the president’s ability to keep pushing legislation in Latin America’s No. 3 economy after a violent outcry over pension reforms he got through Congress late last year.

Macri, who took office in December 2015, is trying to cut Argentina’s fiscal deficit by gradually reducing subsidies for home heating gas and transportation, moves that have triggered an unpopular increase in utility bills and bus fares.

“Mister President, don’t continue with policies that force the most vulnerable parts of our society - retired people, old people - to go hungry,” Hugo Moyano, head of Argentina’s largest umbrella union, the CGT, shouted at an afternoon protest rally.

Union activists danced and beat on drums on Avenida 9 de Julio, the city’s main thoroughfare, under banners representing various labor groups. Traffic was snarled for miles.

Macri aims to cut the primary fiscal deficit to 3.2 percent of gross domestic product this year from 3.9 percent in 2017.

If he presses on with his economic overhaul, aimed at winning the confidence of investors long put off by the high cost of doing business in Argentina, union leaders said they may call a trucking strike next month that could slow the flow of grains from one of the world’s top exporters of soy and corn.

Produce is trucked from Argentina’s vast Pampas farm belt to export terminals clustered along the Parana River in the country’s main grains hub of Rosario. The waterway leads out to the shipping lanes of the South Atlantic.

Macri has promised big changes to labor laws, widely seen as among the most costly to companies in Latin America and a leading obstacle to investment, after his pro-business coalition performed unexpectedly well in October’s mid-term elections.

The president nonetheless lacks a majority in Congress, and his administration was rocked by violent protests over pension reforms in December. Since then he has scaled back unpopular legislation as he prepares to run for re-election next year. He is now taking a piecemeal approach to labor law changes.