As many as 200 students in Cardiff may be denied their vote in Thursday's General Election due to an error with registration.
Cardiff Council said the problem related to students entering "incomplete addresses" when registering to vote.
It said it has found more than a thousand invalid applications, and has contacted around 800 people to put them on the electoral register. But due to a high-volume of queries, it has not been able to contact all of the students affected.
The council said when students are using university halls as their official address, they need to use both their room and flat numbers to register.
The President of the NUS Wales Rob Simkins says he is "alarmed" by the reports. He said he has called on Cardiff Council to ensure the remaining 200 students are added to the electoral register in time for polls opening at 7am on Thursday.
I'm alarmed that a significant number of students may be denied the right to vote because of an administrative error that was no fault of their own. This is the general election that will define our futures and students are demanding that their voices be heard. Cardiff Council must now work with the accommodation provider and the students affected to make sure they are on the electoral register come Thursday. Any other outcome would be unacceptable.
It is the responsibility of the elector to validly register and there is no obligation on the Electoral Registration Officer to chase up invalid applications.
The Electoral Reform Society in Wales have called on a change to the registration process to ensure this does not happen.
Those who have registered in good faith and in good time should not be denied their say due to an address system error. If this is confirmed to be a mistake on the part of Cardiff Council, we would hope the authority do the right thing and rectify this error, rather than risk disenfranchising people through no fault of their own.
The UK goes to the polls on Thursday for the 2019 General Election. Polls open at 7am and close at 10pm.
The first results from constituencies across Wales are expected in the early hours of the morning.
It is the fourth general election in the last nine years.