British labor unions say as many as 2 million border staff, teachers and other public workers will join the country's largest strike in decades.
The walkouts scheduled for Wednesday are predicted to wreak havoc for arriving airline passengers, who could face delays of up to 12 hours at London's Heathrow airport.
Britain's government said Tuesday that nine out of ten schools are expected to close. Ministers warned the strike could cost the economy up to 500 million pounds ($770 million).
Workers oppose government demands that they work longer before receiving a pension, contribute more money to it each month and accept a deal calculated on their average career salary.
Prime Minister David Cameron insisted he won't halt reforms and urged unions to focus on negotiations.