After years of rivalry and poaching each other's members, the National Education Association and the American Federation of Teachers could join forces to create a powerful new organisation representing nearly 3.4 million teachers and associated staff.

Union leaders say the merger is a necessary response to falling confidence in public education and legislative attempts to channel tax money into private schools through vouchers or tax concessions.

Both groups are stressing a "new unionism" that aims to put academic quality and school improvement on the same level as pay, benefits and job security.

They have been working jointly on issues such as teacher quality, discipline and safety.

Convention

The crucial test of the merger proposals will come on July 5, when more than 10,000 delegates to the National Education Association's annual convention vote on them.

The outcome is uncertain. Two-thirds of the delegates must approve the merger, and some large state affiliates are opposed.

The association's president, Bob Chase, says there is a lot of persuading to do in less than a month.

But he adds: "Although there are some who are against it, there's absolutely no reason why we can't get the two-thirds vote."

In the UK, the National Union of Teachers is campaigning for a single teaching union under the banner of "professional unity", but other unions have reservations about such a move.