Students have demonstrated outside the Scottish Parliament against the increased fees for medical students coming to Scotland from England.
Top-up tuition fees will be introduced in England in the autumn
The students said that the fees of up to £2,700 were "a heartbeat away from top-up fees".
Ministers plan to bring in the measure to combat a possible rise in students coming to Scotland when top-up fees are introduced in England in the autumn.
The Scottish Executive said it was opposed to top-up fees in principle.
However, last year Scottish ministers passed the Further and Higher Education (Scotland) Bill which would give ministers the ability to set higher fee levels in order to protect the interests of Scottish students.
The annual fee for undergraduate courses in Scotland is currently just under £1,200 for students coming from outside Scotland.
This would rise to £1,700 under the proposed change, while the fee for medical courses would rise to £2,700.
Most undergraduates domiciled in Scotland have their fees paid for by the Students Awards Agency Scotland.
However, most Scottish graduates pay a graduate endowment, which is a one-off payment at the end of their course.
This is £2,145 for 2005-06 and figures are not yet finalised for 2006-07.
In England from the autumn, annual tuition fees - currently a flat rate of £1,150 - will vary from nothing up to a maximum of £3,000 depending on the institution.
The National Union of Students Scotland has called on MSPs to vote against the increase in Scottish fees, which was being considered in the parliament on Thursday.
Melanie Ward, president of NUS Scotland, said: "Introducing variable fees in Scotland will undoubtedly work against the executive's policy of widening access to students from non-traditional backgrounds, and medicine is one of the areas where these students are least represented.
"Setting the fees for different courses at varying levels is likely to lead to a situation where students choose which course to study based on what they can afford rather than on where their abilities lie.
"We are starting to see the damaging effect of such policies with the introduction of top-up fees in England, and we need to make sure that Scotland keeps market forces out of education."