Neil Shaw, president of the School Leaders' Scotland (SLS) union, says the Scottish Government move will encourage "teaching to the test" and restrict pupil choice.
In January, Education Secretary Michael Russell said candidates sitting Higher English from 2014/15 will answer at least one question on a Scottish novel, play or poem.
The move aims to ensure future generations of Scottish young people grow up with an understanding of their culture and literary heritage.
However, teachers argue they already use Scottish texts alongside established classics, but need flexibility to allow them to follow the interests of pupils.
Mr Shaw, currently head teacher of Boclair Academy in Bearsden, East Dunbartonshire, said: "The compulsory question on Scottish texts in the English Higher exam is potentially limiting for both pupils and teachers.
"I think it is crucial to expose pupils to a variety of Scottish literature as they are growing up. However, we have already had recent concerns from Scotland's exam board that, in some cases, teachers are teaching to the test and pupils are coming to exams with prepared answers.
"If you make any exam question compulsory then that will only encourage further teaching to the test."
Mr Shaw, who will raise his concerns at the annual conference of the SLS in St Andrews today, said the question also ran counter to the principles of Scotland's new Curriculum for Excellence.
He said: "The new curriculum is all about giving teachers more freedom and flexibility and changing that at this late stage is a backwards step. In a modern, outward looking democracy, is it sensible to impose this restriction on our teachers?"
A Scottish Government spokesman said: "The Scottish Studies Working Group considered various representations on the issues of Scottish studies and concluded a specific Scottish element – alongside a wide range of other materials – would be the best way to promote Scottish literature in the classroom, and ensure consistency across all Scottish schools."
In his speech, Mr Shaw is also expected to question the Government's drive towards a Masters level teaching profession.
He plans to say: "Has there been any major piece of research undertaken to support this proposal? We all know, albeit perhaps anecdotally, that not all of our best teachers have the best academic qualifications."