A growing number of universities now refuse to accept the results of resits or give them less weight than those of candidates who take all their exams at once.
Many universities openly admit to discriminating against students taking resits when selecting candidates for a number of courses.
Some refuse to accept resit results altogether, while others say they will only consider them in "exceptional circumstances" or ask for resits results to be higher than their standard offer.
School head teachers have spoken out against the practice, warning that it can be unfair on pupils.
They believe it is actually even more widespread than it appears and that many universities discriminate against resit candidates, but do not acknowledge it officially in their admissions criteria.
Resits are often used by private school pupils who fail to get their required grades and then take a gap year before reapplying the following summer.
Neil Roskilly, from the Independent Schools Association, said: "Universities are increasingly using the resit issue to differentiate between candidates and feel that if they take all their exams at one sitting, they must be better than one who has taken resits.
"I think there are other ways of differentiating and would put more emphasis on the interview.
"There are often valid personal reasons why a student has taken resits and there are not always opportunities to make that known. Sometimes they may not want to."
A spokesman for Universities UK, which represents the country's higher education institutions insisted that there was "no hard evidence" of universities discriminating on the basis of resits "on a wide scale or actually at all".
However, many universities explicitly state such a policy on the internet.
Policies often vary depending on the courses and resit bans are most common with courses such as medicine, law and dentistry.
However, those seeking to study chemistry at Durham, for instance, are warned that although they may still be accepted after resitting "we are looking for students who can pass exams at the first attempt".
At the University of Edinburgh, those applying for courses in humanities and social science are told: "resitting exams can put your application at a disadvantage."
The University of St Andrews warns all students it "expects all the qualifications detailed to be gained at the first diet of examinations".
At Manchester, students relying on resits for any courses are warned: "We may require further information in order to make an informed judgment on your application".
Universities argue that the tactic is needed to help to identify the best candidates. Some are also making increasing use of the A* grade a A-level, which will be awarded for the second time this summer.
Candidates applying to some Cambridge colleges could find themselves needing to obtain at least two A*s.
This year, competition for places is expected to be even more fierce than last year. There are 670,000 applicants for an estimated 487,000 university places. This is increase from 2010 of around 9,000 candidates for the same number of places.
Mary Curnock Chase, the chief executive of the Universities and Colleges Admissions Service, warned students who miss their target grades not to rush into unsuitable degree courses in a bid to avoid next year's tuition fee rise.
She urged potential students to delay their university careers if they fall short of their required grades, even though they will face tuition fees of up to £27,000 as a result.
She suggested that students should not regard the fees as a debt, because the loans are only repaid once a graduate begins earning.
"I would certainly be worried that people might feel that there is more pressure this year. But it would be a real pity if anybody was put off applying for university next year because of the fees," Mrs Curnock Cook said.