LONDON (AP) — Thousands of schools in the U.K. are closing some or all of their classrooms, train services will be paralyzed and delays are expected at airports Wednesday in what’s shaping up to be the biggest day of industrial action Britain has seen in more than a decade, as unions step up pressure on the government to demand better pay amid a cost-of-living crisis.

The Trades Union Congress, a federation of unions, estimated that up to half a million workers, including teachers, university staff, civil servants, border officials and train and bus drivers, will walk out of their jobs across the country.

More action, including by nurses and ambulance workers, is planned for the coming days and weeks.

Britons have endured months of disruptions to their daily lives as a bitter dispute over pay and work conditions drags on between unions and the government. But Wednesday’s strikes mark an escalation of disruptive action across multiple key industries.

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.

Union bosses say that despite some pay rises — such as a 5% offer the government proposed to teachers — wages in the public sector have failed to keep pace with soaring inflation, effectively meaning workers have been taking a pay cut.

The Trades Union Congress said Wednesday the average public sector worker is 203 pounds ($250) a month worse off compared with 2010, once inflation has been 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 rises to slow down this year, Britain’s economic outlook remains grim. On Tuesday, the International Monetary Fund said that Britain will be the only major economy to contract this year, performing worse even than sanction-hit Russia.

Nicola Hawkins, a primary school teacher, said striking was the only way to highlight chronic underfunding in state schools and get the government’s attention.

“It is really difficult to make that decision to walk out, but I’ve come to the conclusion that it is in everyone’s long-term interests really,” she said. “It’s been pointed out that recruitment targets aren’t being met, that teachers are leaving, but our pay has been whittled away over the last decade or so.”

The National Education Union said some 23,000 schools will be affected Wednesday, with an estimated 85% fully or partially closed. Others also on strike range from museum workers and London bus drivers to coastguards and border officials manning passport control booths at airports.

“It's everybody out ... of course there's going to be some disruption and some queues,” Phil Douglas, director-general of Border Force, told reporters. “I don’t rule out further industrial action."

Prime Minister Rishi Sunak's office acknowledged that Wednesday's wave of walkouts will cause “significant disruption” to people, and maintained that “negotiations rather than picket lines are the right approach." But union leaders say the government has refused to negotiate and offer enough to halt the strikes.

Unions have also been angered by the government's plans to introduce a new law aiming to curb strike disruptions by enforcing minimum service levels in key sectors, including health and transport.

Lawmakers on Monday backed the bill, which has been criticized by the unions as an attack on the right to strike.

On Wednesday thousands of people are expected to take part in protests against the bill in London and other cities.