John Johnson, chairman of the National Association for the Teaching of English, said that it was "absolutely integral" to his subject, and called on teachers to resist the move to reduce it.
He said the reason that the task force was against coursework was because it was listening to unions' concerns about teacher workload, rather than to subject associations' concerns about its value.
Last month, The TES reported that the task force, which is drawing up long-term plans for the future of secondary qualifications, is likely to recommend replacing coursework by a single extended research project, in a subject of the student's own choice.
This would form part of a new diploma qualification, covering all subjects, to replace GCSEs and A-levels by around 2010.
Four private-school associations this week published a joint statement expressing "deep scepticism" about the diploma plans, which, they said, could curtail choice in the sixth form and damage individual subjects'
The associations, members of the Independent Schools Council, said that GCSE and A-levels should be retained, but with coursework removed in many subjects and A-levels being separated from the AS.
Pupils should be able to skip GCSEs if they were taking A-levels in the subject, and the overall number of tests and exams should be reduced.
But speaking at NATE's annual conference in Swanwick, Derbyshire, this weekend, Mr Johnson said: "Reflective writing and the chance to look at alternative types of writing are all things that cannot be done in a short test."
Mike Tomlinson, the former chief inspector of schools who is leading the review, told The TES that his group would not do anything which would stop pupils being assessed in areas which were important to the subject.