Police in Stoke-on-Trent are investigating claims that postal votes for the general election may have been tampered with.
They say the returning officer told them 43 papers for Stoke North arrived together and the declaration of identity had been removed from each.
They were all declared invalid. Police were called in on Monday afternoon.
The city council says there is not necessarily anything suspicious about the envelopes.
In a statement, it said: "The votes, which arrived bundled together with an elastic band, all had the declaration of identity removed.
"There is not necessarily anything untoward about the bundle, but the coincidence is sufficient to warrant an investigation by police who are the agency who investigate electoral irregularities."
Staffordshire Police say they will be keeping the Electoral Commission informed.
Joan Walley held the constituency for Labour with a majority of more than 10,000 over the Conservatives.
Last month, five Labour councillors were found guilty of rigging the vote in two wards in the 2004 local elections for Birmingham City Council through mass postal vote irregularities.
An election court judge described the extent of the fraud as something that would "disgrace a banana republic".