MINISTERS are under pressure to reform the way exam appeals are paid for to create a level playing field for pupils.
The Scottish Conservatives said the current system had created a postcode lottery which was unfair on pupils in some areas.
The call comes after the introduction of a new system of exam appeals was introduced last year by the Scottish Qualifications Authority (SQA).
The SQA introduced charges for the first time to cut down on bogus appeals as part of a wider shake-up of the system.
The new costs range from £10 for a check to see if the marks have been added up correctly to £39.75 for a full review.
Although no charge will apply if a mistake has been made it is up to local authorities to decide whether the costs are paid for out of central funds or taken from school budgets.
Liz Smith, the Conservatives young person spokeswoman, said some pupils may be disadvantaged if they live in communities where schools are struggling with tight budgets.
She said: "In February last year I raised concerns that the new system had within it an inherent unfairness which would disadvantage some pupils and I now firmly believe this to be the case.
"I have written to Education Secretary Angela Constance to ask her to take action to address this concern because it is surely essential that no pupil - irrespective of which school he or she attends - is in anyway disadvantaged.
"Requests to review marking must be decided on sound educational judgment and not on the financial circumstances of different schools and local authorities or on the ability of parents to pay."
Meanwhile, unions have warned that greater numbers of teachers are set to take early retirement as a result of workload pressures associated with the roll-out of the new Curriculum for Excellence.
Larry Flanagan, general secretary of the Educational Institute of Scotland (EIS) said: "A lot of long-serving teachers are worn down by it all and have decided it is a good point to exit."
However, Scottish Government figures show the number of teachers retiring actually fell in the last school year with numbers dropping from 2,307 in 2013/14 to 2,267 in 2014/15.
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