LONDON — Thousands of schools in the U.K. closed some or all of their classrooms, train services were paralyzed and delays were expected at airports on the biggest day of industrial action Britain has seen in more than a decade, as unions stepped up pressure on the government Wednesday to provide better pay amid a cost-of-living crisis.

The Trades Union Congress, a federation of unions, estimated that up to a half-million workers, including teachers, university staff, civil servants, border officials and train drivers, went on strike across the country.

More walkouts, including by nurses and ambulance workers, are planned for the coming days and weeks.

Thousands of demonstrators wave banners Wednesday as they stand near Downing Street in Westminster in London. Kirsty Wigglesworth/Associated Press

Months of strikes have disrupted the daily routines of Britons as a bitter dispute between unions and the government over pay and working conditions drags on. The simultaneous strikes across multiple industries on Wednesday marked an escalation of the unions’ protest actions.

The last time the country saw mass walkouts on this scale was in 2011, when well over 1 million public sector workers staged a one-day strike in a dispute over pensions. Others on strike Wednesday ranged from museum workers and London bus drivers to coast guard personnel and officers who staff passport booths at airports. The British Museum was closed Wednesday because of the strikes.

Union bosses argue that despite some pay increases, such as a 5% offer the government proposed to teachers, the U.K.’s soaring inflation has plunged scores of public sector workers into financial difficulty because their wages have failed to keep pace. Teachers, health workers and many others say their wages have fallen in real terms over the last decade, and the surge in living costs that began last year exacerbated the problem.

The Trades Union Congress, or TUC, said Wednesday that the average public sector worker is 203 pounds ($250) a month worse off compared with 2010, once inflation is taken into account.

Inflation in the U.K. stands at 10.5%, the highest in 40 years, driven by skyrocketing food and energy costs. While some expect price increases to slow this year, Britain’s economic outlook remains grim. On Tuesday, the International Monetary Fund said the country will be the only major economy to contract this year, performing even worse than sanctions-hit Russia.

The National Education Union said some 23,000 schools would be affected Wednesday, with an estimated 85% fully or partially closed.

“The government have been running down our education (system), underfunding our schools and underpaying the people who work in them,” Kevin Courtney, the NEU’s joint general secretary, said. “Primary schools where you can’t find special needs assistants, because they’re taking jobs in supermarkets where they are paid better. That’s what’s making people take action.”

Prime Minister Rishi Sunak told lawmakers that teacher strikes were “wrong,” and claimed his government had already given teachers their biggest pay raise in 30 years.

“Our children’s education is precious, and they deserve to be in school today,” he said.

His office argued that pay increases for public sector workers would not be affordable for taxpayers and could lead to tax hikes, more government borrowing or spending cuts elsewhere.

Union leaders blame the government for refusing to negotiate and offer enough to halt the strikes.

Workers were also angered by the government’s plan to introduce a new law aiming to curb strike disruptions by enforcing minimum service levels in key sectors, including health and transportation. Unions have criticized the legislation as an attack on the right to strike

Lawmakers backed the bill on Monday. Thousands of people turned out in London, Manchester and other cities Wednesday to protest the proposal.

TUC General Secretary Paul Nowak said industrial unrest would continue until the government puts an acceptable pay offer on the table.

“The message to the government is that this is not going to go away. These problems won’t magically disappear,” he said.