An investigation has been launched after a councillor allegedly complained that a voter with learning difficulties "shouldn't be voting".
Officials at Trafford Council in Manchester say they have been made aware of the incident, which allegedly involved an unnamed councillor at a polling station yesterday.
The accusation was made by Kate Green, Labour MP for Stretford and Urmston and shadow spokesman for disabled people.
Disabilities charity Mencap said the allegations were concerning.
UKIP's successes in the local elections have raised the possibility of them winning a Westminster seat at the general election.
A year ahead of the general election, Ed Miliband's party is seeing only patchy support in areas it should expect to gain ground.
UKIP are likely to make Rotherham a key target for 2015 after a storming result in the local elections.