ATHENS — Thousands of Greeks walked off the job Tuesday in a 24-hour general strike called by unions opposing a new round of austerity measures that the government has vowed to enact at the urging of the country’s foreign creditors. The sorest point is a much-delayed overhaul of the Civil Service involving thousands of layoffs and wage cuts, which is set for a vote in Parliament on Wednesday night. The package must be passed if Athens is to secure the first installment of $9 billion in rescue loans approved last week by euro zone finance ministers.

Despite strong objections by the political opposition, and by some deputies in the ruling coalition, the package is expected to squeak through the 300-seat Parliament where the government has a slim majority of five. Implementation of the contentious reforms will remain a tough challenge however in a volatile political climate.

The nationwide walkout, called by the country’s two main labor unions, which represent some 2.5 million workers, shut tax offices and other government services, reduced hospitals to emergency staff and disrupted travel. Trains remained in depots and international flights were suspended between noon and 4 p.m. as air traffic controllers joined the action. Public transport workers were running a reduced service to allow Greeks to join protest rallies planned for Athens and other major cities.

The unions’ appeal drew some 16,000 demonstrators onto the streets of the capital, according to a police spokesman who said the rally was “entirely peaceful.” Strikes have become a frequent occurrence as Greece’s economic crisis continues into its fourth year. The turnout Tuesday was moderate by Greek standards, in part because many people, particularly students and civil servants, have left Athens for their villages for the summer break.