Hundreds of students are preparing to take part in rent strikes after paying for "hardly used" rooms during the pandemic.
Some Welsh universities have already offered refunds to students who have been living away due to Covid-19.
But students in Cardiff, Swansea and Bangor claim they are being treated unfairly and are threatening to withhold rent.
Universities said they were trying to work out the implications of Covid-19.
And a solicitor warned students they could face legal action for not paying rent, with long-term implications possible if they lose.
Face-to-face teaching was suspended and many students moved back home before Christmas as coronavirus cases continued to rise.
Staggered returns are being introduced in order to "help stop the spread of the virus in student accommodation", according to the Welsh Government.
Students attending universities across Wales had demanded rent rebates.
They said they had not been living in the rooms or using facilities, despite paying for them, because they were abiding by Welsh Government guidelines.
Cardiff Metropolitan University, Aberystwyth University, Swansea University, Bangor University and Cardiff University have now offered eligible students rebates or discounts for time not spent living on campus.
University of South Wales said it will be offering a "rent holiday" on university-owned accommodation in Treforest, Rhondda Cynon Taf, for the period 4 January to 12 February.
University of Wales Trinity Saint David (UWTSD) said on Thursday it is now offering refunds to students who have not returned to university-owned accommodation while teaching is solely online.
But students say the offers are inadequate for students already paying £9,000-a-year tuition fees at a time when most of the teaching was online, and they had been unable to use facilities in halls.
While the students cannot hold their protests in person due to coronavirus laws, hundreds are now planning to cancel their direct debits, withholding thousands of pounds of rent from universities.
Michelle Francis, who formed the Bangor Rent Strike campaign, said the university's offer of a 10% discount to eligible students living in university-owned accommodation did not go far enough.
She said students who had chosen to go home for Christmas were not eligible, despite being unable to use facilities paid for during the first term.
"[We were] advised to have left university from the beginning of December and to come back at 8 February," she said.
"That's 25% of our halls that we've been paying and we're not there... we should be allowed to have that back."
So far over 300 students have joined the campaign to cancel their direct debits paid to Welsh universities and campaigners said the numbers were growing daily.
On Wednesday, Cardiff University joined other Welsh universities in offering a rent rebate to students living in university-owned accommodation during the pandemic.
But the full rebate, for the time students are unable to return to live in their accommodation, will not be applied until April.
Swansea University has also confirmed a rent reduction to students in university halls who have been asked to remain at home.
Oisin Mulholland of Swansea Rent Strike said the group wanted the university to commit to fairly "assessing the situation", including for the coming term, and students who had already moved in should be given rebates as well.
"There was a window in January, where the Welsh Government said return, but the English government said don't return, and the university said nothing," he said.
"Many students came back and are now trapped in Swansea and can't go back because of lockdown"
Ibrahim Khan, of the Cardiff Rent Strike campaign, said the rebate was "too late" for students struggling financially now.
"The university should be giving us the rebate this January as opposed to the third instalment in April," he said.
Lawyers have warned that students would in breach of contract if they cancel the direct debit for their rent.
Siôn Fôn, a solicitor at Darwin Gray, encouraged students to discuss the issue with their families and student unions before taking action.
"I think a case could be brought forward pretty easily against somebody not paying rent," he said.
But he said students may have a case against the university due to not being able to access advertised facilities, but if the university took legal action it could have long-term consequences for individuals.
"If the students lose, and even after losing don't pay the rent, that would come up on credit scores, or with the bank, if they're trying to get a mortgage or a credit card it would come up on their record," he warned.
A spokesperson for Cardiff University said technical reasons meant they had to wait until the April instalment of accommodation fees to provide the rebate.
Swansea University said some students had already returned when the stay at home guidance was issued, and it was working through the "implications of this".
"To help with this the university will not generate invoices for any students with university accommodation until May when we have been able to look at these cases," a spokesman said.
Bangor University said it did not wish to add anything further following its rebate announcement.
The Welsh Government said it had provided an extra £40m to help universities, including £10m for towards student hardship and support.
"It would seem fair that students should be eligible for a rebate for the period when a course is online only and we welcome moves by universities to address this," a spokesman said.
"We are actively considering how we can support our students and universities even further."