Under the changes,humanities and communications courses will more than double in price,with a full year of study costing $14,500. Fees for law and commerce will increase 28 per cent to $14,500. Teaching,nursing,clinical psychology,English,languages,maths and agriculture courses will drop by 46 to 62 per cent,costing $3950.

Greens education spokeswoman Mehreen Faruqi said the modelling showed many young students would have unpaid HELP debts well into their 40s and it was conceivable that some may never fully pay it off.

"This is yet another reason for the Senate to reject this bill in its entirety,"Senator Faruqi said."From its funding cuts and punishment of struggling students,to its failure to create enough new places and disproportionate impact on women,this bill is a cruel,illogical mess that can’t be fixed."

Education Minister Dan Tehan said the intent of the funding overhaul was to encourage students to study units in maths,English,IT and a number of other disciplines to boost their employment prospects. The fees are set at subject level,rather than degree,meaning students can incorporate studies from cheaper categories.

"Senator Faruqi has not included in her modelling the 60 per cent of students who will pay less or see no change to the cost of their degree,"Mr Tehan said.

"The senator has not modelled how much faster they will repay their HELP loan under'Job-ready Graduates'. This is selective modelling at its worst. Maybe Senator Faruqi should study a mathematics unit."

New data released by the government on Sunday showed graduates of medicine,dentistry and pharmacy had the best employment prospects,with 97.3,98.3 and 95.7 per cent respectively employed full-time three years after leaving university. Graduates in creative arts,humanities and communications had the weakest prospects,with 79.4,87 and 84.9 employed respectively.

Following extraordinary public criticism of the overhaul by Regional Education Minister Andrew Gee,a Nationals MP,Mr Tehan last week revised the package to cut the fee hikes for social work and psychology subjects.

Australian National University economist Bruce Chapman,the architect of the HECS student loan system,has questioned if the fee changes will have a lasting impact on student choices because the cost is deferred and discounted thanks to the availability of long-term,interest-free loans.

In his submission to the consultation process on the government's package,Professor Chapman said it was"difficult to believe that students particularly keen on pursuing studies and careers in particular broad areas ... would consider a significant switch to quite a different area"because of the changes.

His own calculations found a $20,000 fee hike for a humanities degree would mean increased repayments of only"$4 a week,around the price of a cup of coffee"for a female graduate on a median income.

Mr Tehan has expressed confidence the price signal will have an impact,saying enrolments in maths and science doubled a decade ago when the student contribution was discounted.