The London Association for the Teaching of English claims the curriculum at seven, 11 and 14 is dominated by tests which fail to provide reliable information about how pupils are doing.
John Wilks, general secretary of LATE, said: "The increasing status given to SATs results through league tables and performance management is encouraging teachers to teach to the test. There is a real danger that the curriculum will become increasingly narrow."
About 11,000 teachers are needed to mark the English, maths and science tests, taken in May by 11 and 14-year-olds.
LATE has called on teacher unions and professional associations to organise a boycott.
The National Association for the Teaching of English has called for national tests to be replaced by moderated teacher assessment.