BRASILIA – The general strike called for Friday by Brazil’s principal labor unions against the president’s austerity program began taking effect across the country from the early hours, though with different degrees of support.

The effectiveness of the strike in most of the 27 regional capitals was due to the support of transport unions, which stopped many people from getting to work including many opposed to the protests.

According to local officials, the strike is strongest in Sao Paulo, the financial and industrial heart of the country and also the stronghold of the largest labor unions, most of which have joined in the shutdown.

Burning tires were used to barricade a road leading to the Sao Paulo-Guarulhos International Airport, on the metropolis’ outskirts, although police managed to clear the route after a face-off with protesters.

That action was promoted by the civil aviation union and the Homeless Workers’ Movement.

Roadblocks also were established on other key highways in Sao Paulo state, including Via Dutra, which links the cities of Sao Paulo and Rio de Janeiro.

Most Sao Paulo Metro drivers were supporting the general strike, the first in two decades, leaving all but one of the five main lines out of service.

In Rio de Janeiro, transport workers provided less support and the strike was not as intense, while in Brasilia there were few buses to be found in service, and the walkout affected even the public sector.

The Esplanade of Ministries, an avenue in Brasilia where most government buildings are located, was closed to traffic early on for security reasons, while security measures were stepped up in anticipation of the marches expected throughout the day.

The main cause of the protests is President Michel Temer’s drive to overhaul labor law and the pension system.

The labor-law overhaul, which was passed by the lower house on Wednesday night but still needs Senate approval, would usher in lower labor costs for businesses and lend legal legitimacy to contracts reached by companies and workers via collective bargaining.

Those contracts would be valid even if they contradict some aspects of the labor code providing strict workers’ rights protections.

The labor-law vote is seen as a test case for a vote on a pension overhaul, a legislative package that also is opposed by unions but strongly backed by the business sector and Temer’s administration, which says it would substantially reduce government spending.

Temer also has angered many Brazilians by signing into law a spending cap that limits public spending to inflation for the next 20 years, an austerity package that comes even amid a deep recession and with a record 13.5 million people currently unemployed.

Last month, Brazil’s Congress also approved a controversial bill that allows companies to outsource any job.