Police in Bradford are now examining 252 cases of alleged electoral fraud, prompting calls for an "urgent review" of the postal voting system.
Two men, aged 38 and 51, have been quizzed by police as part of an inquiry into postal ballot irregularities.
The arrests relate to some of the cases that have now been passed on to West Yorkshire Police, Bradford City Council revealed on Wednesday.
Returning officer Philip Robinson said a review was needed before 2006.
In a statement, Mr Robinson said: "A total of 252 cases have now been referred to West Yorkshire Police for further investigation as to whether any electoral fraud has occurred.
"There have been two arrests made by the police in connection with their investigations into some of these cases.
"The referrals and arrests follow joint action by elections staff and the police. It was made clear at the outset that both would be working closely together to prevent and detect any fraud in the electoral process.
"It is essential, given the experience here and elsewhere across the country, that urgent reviews of electoral registration and postal voting on demand are undertaken in advance of the next elections in 2006."
Detectives launched their inquiry last month after allegations made against Conservative councillor Jamshed Khan, 51.
A newspaper claimed 13 people had applied for a postal vote at his Bradford home, while another 12 people had registered to vote at a derelict house that he co-owned until last year.
Mr Khan insisted allegations of postal ballot were false and said he would be "seeking legal advice" over the claims.
He also said the allegations of fraud regarding the derelict house had "nothing to do with him" because he did not own the property.
West Yorkshire Police confirmed they were continuing to investigate a number of cases.
A spokesman said: "A team of officers are continuing to investigate allegations of electoral fraud and a number of matters have been brought to our attention in various parts of the county."