SANTIAGO, Chile — Chile is bracing for a nationwide, two-day shutdown as unions, students and center-left political parties demand fundamental changes in society.

They want to replace Chile’s dictatorship-era Constitution, which concentrates vast power in the presidency, with a new charter enabling popular referendums and making free quality education a right for all citizens. They also want pension reforms, a new labor code and more health care spending.

Chile’s largest union coalition called the strike for Wednesday and Thursday to join forces with the high school and university students boycotting classes for three months now. They have support from the center-left coalition that governed Chile for 20 years before President Sebastian Pinera brought the right wing back into the presidential palace last year.

Transportation workers and day-care providers also plan to strike, stranding millions of other Chileans.

“It’s painful to see those working so hard to paralyze Chile,” Pinera complained Tuesday. “We are perfectly conscious that our country has many unpaid debts, that there are many problems that remain unresolved, many of which were caused decades ago.”

Chile’s economy could lose $400 million — a disappointing setback, “especially now with huge storm clouds appearing in the global economy,” Pinera said.

Chile’s GDP is growing at a healthy 6 percent, and the government has $24 billion in foreign reserves in its rainy day fund, but Pinera has warned against “the temptations of populism and irresponsibility.”

“Nothing is free in this life; somebody has to pay,” Pinera said when he proposed a 21-point education reform package to Congress this month.

The package includes $4 billion in new education funding, more scholarships, more teacher training, help for students who can’t pay their loans and a reduction from 5.6 percent to 2 percent in student loan interest rates. He also proposed a new government agency to take over and fund failing local schools, and an effort to make private universities comply with Chile’s law requiring nonprofits to reinvest their gains.

But Pinera has drawn the line at more fundamental changes and flatly rejected the idea of popular plebiscites. Providing free education for everyone would mean forcing the poorest to help subsidize the most fortunate, he argued.

Chile spends $2,000 annually per schoolchild, compared with $7,500 in the most-developed countries, according to the multinational Organization for Economic Cooperation and Development, which Chile joined as it tries to leave the third world behind.

Education in Chile also has relied more on private funding than in any other member country, according to a 2004 OECD study.

Chile’s government spent just 0.4 percent of its GDP on education, while student family contributions and bank loans made up another 1.8 percent, for a total of 2.2 percent of GDP. By comparison, the U.S. government spent 1 percent of U.S. GDP on education, leaving private sources to make up another 1.8 percent.

In other words, Chile’s government provided 18 percent of the money spent on education in the country, compared to 36 percent in the U.S. In most other developed countries, the government assumes much more of this burden, providing 71 percent of the total education spending on average, enabling families to spend and borrow much less to see their children get ahead.

Chile’s 3.3 million schoolchildren include 54 percent who attend local schools, whose quality depends on municipal funding, and 31 percent who attend state-subsidized private schools, whose quality largely depends on parent income. A luckier 9 percent attend nonprofit schools, often subsidized by corporations, and 6 percent attend private schools.

Pinera’s ministers have called protest leaders intransigent, but polls suggest most Chileans support their call for deeper reforms.

Chadwick dismissed the demands as “more than utopian,” and said the palace doors “have always been open” to labor leaders seeking dialogue. But such openness hasn’t extended to the student movement.

Legislative leaders have proposed a negotiating process that includes students and teachers as well as the government, but Pinera refused to sit down with the protesters before submitting his proposed changes to lawmakers.

Students delivered a letter to the palace Tuesday asking for Pinera’s direct intervention to resolve the conflict. University of Chile student leader Camila Vallejo described it as a plea for Pinera to clarify whether “he really has the willingness to see education as a universal social right, and not as a consumer good, as he has suggested.”