The impact of university lecturer strikes should be taken into account in students' grades, NUS Wales has said.
Lecturers at four Welsh universities joined thousands across the UK in 14 days of industrial action in a dispute over pensions, with more planned.
Some students have joined a potential UK-wide class action for compensation.
Cardiff University said it was "sorry" but it had "worked hard" to mitigate disruption.
However, a group of its postgraduates plan to withhold fees over missed teaching.
Students at Aberystwyth, Bangor and Cardiff universities, along with those at the University of Wales, have been affected by the industrial action which has taken place since January, alongside 57 other institutions around the UK.
Staff are angry at plans to change the Universities Superannuation Scheme (USS ) from a defined benefit scheme, where they would have a guaranteed income in retirement, to a defined contribution scheme, where their pensions would be subject to changes in the investment markets.
NUS Wales president Ellen Jones: "I think the impact of the strikes should be taken into consideration when assessing students and when they are having to do exams but this should be in extenuating circumstances.
"We know that exams and assessments can be a very stressful time but we also believe that [having] well-funded lecturers is essential to having an excellent student experience."
Harry Thompson, of Brecon, Powys, has missed 36 hours of teaching from his one-year master's course in political communications at Cardiff University.
He is one of more than 80 postgraduates at Cardiff University who have pledged to withhold their fees due to missed teaching.
Mr Thompson said: "We haven't had the tuition the tuition fees are for so we're proposing to hold back £2,000 from our next payment until the university makes some proper concession."
He said the campaign group believed lecturers were "forced into" strikes by the university and they were in full support.
Students from Cardiff and Aberystwyth universities are among several hundreds from the UK who have joined a potential class action against the institutions alleging a breach of contract, being proposed by law firm Asserson.
The firm said it needed at least 5,000 UK students to sign up to make the funded action viable but it was confident it would happen.
Partner Trevor Asserson said: "We know the burden that falls on students by the time they leave university - it's a very significant amount of money.
"And not to get value for money, when you're taking that kind of risk in your career going forward… they are actually a group of people who we think deserves the assistance of the courts and the legal system."
A Cardiff University spokesman said: "We are very sorry this situation has arisen and have worked hard to provide students with a clear understanding of what mitigating actions will be taken to address the disruption caused by the industrial action."
He said assurances had been made that exam boards would take into account all "direct disruption" from strikes without students needing to report them as extenuating circumstances.
The university said it expected "all tuition fees to be paid" as failure to do so could result in students being withdrawn from their courses.
It added any student wanting to claim compensation would have to show the university had not taken "reasonable steps" to provide them with an opportunity to demonstrate achievement in their course.
An Aberystwyth University spokeswoman said: "The university is working hard to minimise the impact of the industrial action through detailed contingency planning with the aim of ensuring that students are not disadvantaged, and are able to achieve the learning outcomes of their modules and progress in their degree programme.
"Where we believe there has been impact, appropriate adjustments will be made through assessment or moderation processes at module level to ensure all students are treated fairly and consistently."