David Blunkett is set for a show-down with teachers over threats of industrial action against the rising number of staff shortages.

From today the NUT and NASUWT will not cover unfilled posts or staff sickness for more than three days.

The education secretary is said to be considering a series of emergency measures including bringing in non-union staff, increasing supply cover and recruiting more teachers from abroad.

Blunkett has hinted that he may opt for a direct confrontation with the teaching unions. "The government is looking at ways we can deal with the unions in a way they could be surprised about. We will do anything we have to help schools overcome this problem. Teachers who are prepared to cover are going to feel really aggrieved with those who walk away. In one breath they want to be treated as professionals yet in the next they act in a really unprofessional way."

Doug McAvoy, NUT General Secretary, dismissed the education secretary's remarks. "With around 3,000 vacancies in London alone and an estimated 10,000 round the country teachers are being exploited and children's education put at risk. The government angers teachers by continuing to deny there is a staffing crisis.

"Our action will expose this deceit. Parents have a right to know when teacher shortages are short changing their children's education. The government must act by setting up an independent inquiry into teachers' pay levels, structure and conditions of service," he said.