America’s largest teachers’ union sued the White House last week, for under-funding its education reforms and placing unreasonable demands on schools.

The challenge could be the most far-reaching yet to the Bush administration’s embattled No Child Left Behind Act, and comes amid a mounting US-wide revolt against the legislation. Last week, Utah lawmakers voted to give priority to their own education policies, while Connecticut officials reaffirmed plans to take the administration to court.

The lawsuit from the National Education Association (NEA), which represents 2.7 million staff, could fundamentally affect the progress of the most radical school reforms in a generation.

The Act holds schools to an intensive test-based accountability system, imposing sanctions for failure.

To redress underachievement among minority and low-income pupils, the legislation forces schools persistently missing test targets to pay bus fares for pupils to attended a stronger school. They should also meet the cost of external tutoring selected by parents.

But critics charge that the White House has short-changed education authorities in funding the reforms, forcing them to divert money from other programmes.

At the heart of the NEA’s case is language in the statute itself absolving states of requirements to “incur any costs not paid for under this Act”.

This offers a strong potential get-out clause, said Goodwin Liu, assistant law professor at the University of California, Berkeley.