A Welsh university has set up an in-house coronavirus testing service and is “strongly urging” students arriving in September to use it.
Cardiff University said students would be invited to take part, but testing would be voluntary.
Swansea University said it had considered it but decided against it on the advice of the local health board.
The Welsh Government said it had not recommended in-house testing and it was up to universities to decide.
It comes as the academics’ union UCU said the movement of a million students around the UK could prompt an “avalanche of infections”.
The union wants universities to scrap plans for face-to-face teaching until Christmas.
How the Cardiff testing service would work was set out in an email to students from pro vice-chancellor Claire Morgan.
She said on arrival they would be “invited to attend one of our testing stations.”
“The test is very safe and nothing to worry about,” Ms Morgan said.
“While the test is voluntary, we would strongly urge you to participate and help to protect our Cardiff community.
“The greater the engagement from you all, the greater the impact the testing service will have in terms of keeping us all safe.”
Anyone testing positive would need to self-isolate, Ms Morgan said.
“If they live with others, all other household members must also stay at home and self-isolate,” she added.
“We are working closely with the NHS to provide additional support should it be required.”
Cardiff University said it was “preparing meticulously” for students’ arrival.
“Discussions about introducing our own testing service and how to put in place the necessary links into the NHS are ongoing with the public health authorities,” a spokeswoman said.
Swansea University’s chief operating officer Andrew Rhodes said it had decided against setting up an in-house testing service after a meeting with Swansea Bay University Health Board.
“They were clear they would absolutely not support the university running their own testing programme, which is why we’re not,” he said.
“They were clear the tests would not have been part of the test, trace, protect system.”
Aberystwyth University said it was working to “agree an approach to testing for Covid which reflects Welsh Government guidance.”
Both Cardiff Metropolitan University and the University of South Wales said they would not offer in-house testing.
Wrexham Glyndwr University said it was not “insisting” students were tested.
Bangor University and the University of Wales Trinity Saint David have been contacted for comment.
National Union of Students Wales president Becky Ricketts said staff and students’ health must be “the number one priority” for universities.
“Any student or staff member engaging in in-person learning should be regularly tested and have access to local testing,” she said.
“We urge the Welsh Government and universities to work together to consider how this can be achieved across the whole of Wales.”
The Welsh Government said it had not recommended in-house testing, but it was up to universities if they wanted to do that.
It said it would look to “target testing where health surveillance highlights increased risk”.
Guidance has been published setting out how universities can reopen while meeting guidelines designed to stop the spread of the virus.