MSPs are to be urged to ensure free musical tuition for children after it emerged pupils pay almost £3 million to councils each year.
Teachers' union the Educational Institute of Scotland (EIS) will argue the case as part of a Holyrood investigation.
Figures obtained by the EIS under freedom of information legislation showed disparity across Scotland's 32 local authorities.
Aberdeen City Council charges as much as £340 a year while others, including Glasgow and Edinburgh councils, charge nothing.
In a submission to Holyrood's Education and Culture Committee, the EIS stated: "The responses received from local authorities point to a huge variation in charging practices. It is our view that the teaching of instrumental music and voice should be free to all students.
"This will ensure a standard provision across Scotland, thereby allowing individuals to achieve their full potential, regardless of their geographical location or financial circumstances."
The EIS instrumental music teachers' network was established to protect and develop instrumental music and vocal teaching in Scotland. The group argues that instrumental music is central to national musical heritage, although it can be "overlooked".
Six councils charged students entered for SQA music examinations.
Eight local authorities do not charge for instrumental tuition. Out of the 24 which do, charges range from £95 to £340.
The net revenue generated for each council ranges from none to more than £530,000, the EIS said.