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.
The Electoral Reform Society in Wales have called on a change to the registration process to ensure this does not happen.
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.