RIO DE JANEIRO — A general strike disrupted cities around Brazil on Friday as unions marshaled resistance to austerity measures proposed by the scandal-ridden government of President Michel Temer, reflecting his struggle to persuade voters that his proposals to overhaul pension systems and labor laws are necessary.

Tensions flared in Rio de Janeiro, with schools warning parents to keep students at home, security forces using tear gas on protesters at ferry terminals near Guanabara Bay and clashes erupting in Santos Dumont Airport. In São Paulo, Brazil’s largest city, protesters blocked highways, halted much of the public transit network and shut down access to an array of public buildings.

The strike also hit cities elsewhere in Brazil, including Porto Alegre, Belo Horizonte and the capital, Brasília, though many businesses in the country were still able to open on Friday, at least partly, or operate at a slower pace than usual.

“The strike is completely justified, but I’d be fired if I didn’t go to work,” said Marco Basaglia, 48, a bank employee in São Paulo who walked to work Friday instead of taking public transportation. “Temer hates working people. This is the worst government Brazil has ever had.”