Teachers will go on strike for the first time in two decades later this month, their union announced on Tuesday, escalating a bitter pay dispute.

The National Union of Teachers called the strike for April 24 after rejecting the government's three-year pay deal. A third of teachers voted in the ballot, although the NUT is the only union supporting the action.

If carried out, it would be the first national teachers' walkout in 20 years, the NUT said.

The government urged the union to reconsider, saying a strike would "disrupt children's learning, inconvenience parents and place a burden on fellow teachers".

It creates another headache for Prime Minister Gordon Brown after previous salary disputes with police and government departments and after MPs had to accept a below-inflation pay rise.

"NUT members have voted 3:1 in favour of industrial action," the NUT's general secretary, Steve Sinnott, said in a statement.

"I call on the government to think again and ensure that salaries at least keep pay in line with inflation and that there is a recognition of the continuing workload pressures on teachers," he added.

The schools secretary, Ed Balls, has said teachers' salaries would rise by 2.45 percent from September 2008 and by 2.3 percent from September 2009 and in 2010.

The 2.45 percent rise is higher than government's targeted Consumer Price Index inflation rate of about 2 percent, although it is lower than the Retail Price Index - at present 4 percent - on which most private sector pay deals are based.

A Department of schools spokeswoman said the pay award was recommended by the independent School Teachers Review Body.

"The government accepted this advice in full," she said.

"It was welcomed by all the other teaching unions.

"So it is disappointing that a small proportion of teachers are threatening to disrupt children's education in this way."