Scores of children's authors have declared their support for the Sats boycott by primary headteachers and condemned Ed Balls' attempt to stop it.
A letter signed by 87 authors, including former children's laureate Michael Rosen and Roald Dahl Funny Prize winner Philip Ardagh states: "We deplore Government threats to use legal action against a form of action which will give children more time to learn and will not disrupt their education in any way."
Mr Balls has said that he is consulting lawyers over whether to mount a legal challenge after the NAHT and NUT confirmed their members will not administer the tests, due to take place in the week beginning May 10.
The Authors Against Sats campaign, which began in 1993, has called for the tests to be scrapped saying they stifle empathy, imagination and creativity.
Campaign organiser Alan Gibbons said: "The testing regime means fewer and fewer books are read in practice. Although teachers in many schools heroically try to pursue reading for pleasure, the roller coaster of optional tests and then Sats means reading by choice becomes more marginalised compared with 15 or 20 years ago and that is damaging."