Thousands of schools in the UK have closed some or all of their classrooms, train services have been paralysed and delays are expected at airports in what is shaping up to be the biggest day of industrial action Britain has seen in more than a decade.

Unions are stepping up pressure on the government to demand better pay during a cost-of-living crisis that is wreaking havoc on the personal finances of most Britons.

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 – walked off their jobs across the country on Wednesday.

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

At the heart of the strikes is a bitter dispute over pay and working conditions that is dragging on between unions and the government. Wednesday’s strikes mark an escalation.

The last time the country saw mass walkouts on this scale was in 2011 when well over one 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 percent 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 that the average public sector worker is 203 pounds ($250) a month worse off compared with 2010 once inflation has been taken into account.

Skyrocketing food and energy costs have caused inflation in the UK to soar to 10.5 percent, the highest rate in 40 years. While some economists expect price rises to slow down this year, Britain’s economic outlook remains grim.

On Tuesday, the International Monetary Fund said Britain will be the only major economy to contract this year, performing worse even than sanction-hit Russia.

The National Education Union said about 23,000 schools will be affected by Wednesday’s strikes with an estimated 85 percent fully or partially closed.

Other workers on strike range from museum workers and London bus drivers to coastguards and border officials manning passport control booths at airports.

Mick Whelan, general secretary of the train drivers union ASLEF, said the government must listen to workers’ demands.

Former Labour leader Jeremy Corbyn, who joined striking workers on a picket line, told Global News Insight that the next government will have to increase wages and find the money to do so.

“They will have to do it, and they will have to raise the money to not just pay the teachers but fund the schools as well because that’s a key part of it,” Corbyn said. “It can be done by a fairer system of taxation and realising that this country cannot afford the levels of inequality we have.”