A leading disability charity has told BBC Wales people with learning disabilities are sometimes being denied their chance to vote.
Stephen Thomas (right) had planned who he would vote for
Mencap Cymru cite the case of Stephen Thomas, 25, of Prestatyn, who has Down's Syndrome, has studied politics and had chosen his candidate.
But he was told there was nobody to help him read the ballot papers.
Denbighshire council says it is investigating but disputes the family's version of events.
At the polling booth, Mr Thomas' parents say they were asked if he was capable of voting at all.
Officials said there was no-one available to help him read the ballot papers so he could cast his vote.
Mr Thomas said: "I'm feeling upset about it.
"I couldn't go for the vote. I can't understand the questions.
"People can help me by reading the questions to me."
Mr Thomas' mother Susan told BBC Wales she was very embarrassed by the situation.
"Everybody was looking and listening to what was going on.
"We had no privacy whatsoever. We just wanted to get out of there.
"When we got there, I handed my card in and asked would it be alright for Stephen to vote.
"The returning officer asked if he'd be able to understand the questions.
"I said I didn't know, it was his first time.
"I asked would I be able to help him, not to influence him, but to help him read the questions."
She was told no, and that the returning officer could not read the questions either.
"By this time, the queue of voters was getting longer - they were looking and listening to everything that was going on.
"I was embarrassed, upset and angry."
The charity has said Mr Thomas' case was not unique.
They say they have several other incidences of people with learning disabilities being unable to vote because the necessary help was not offered at polling stations.
Mencap Cymru has lodged an official complaint with Denbighshire council over Mr Thomas' claims.
Denbighshire's chief executive and returning officer Ian Miller has investigated the complaint and is due to respond to the charity shortly.
He said: "Many elements of the complaint are not borne out by the evidence from the electoral staff.
"In particular, the electoral staff state categorically that the young man was not refused a vote, and I would not accept the suggestion that he was treated unfairly.
"There are clear rules in electoral law about formal questions that are put to a person in cases where there is doubt about the identity of the individual.
"The questions can also be used if there is doubt about a person's ability to understand the process, for example if someone appears to be under the influence of drugs or alcohol.
"In this case, the young man's mother appears to have decided herself that her son was not going to vote before electoral staff had the chance to put the formal questions to him."