A 50-year-old woman has been arrested after police recovered a large number of postal voting forms at an address in Bordesley Green, Birmingham.
Officers monitoring potential fraud in the local elections carried out the raid in Ronald Street and in Hob Moor Road, where more items were found.
The woman has been arrested on suspicion of conspiracy to defraud the local election process in Birmingham.
The local elections are due to be held on 4 May.
The BBC has learned the arrested woman is the wife of a Lib Dem candidate standing in the forthcoming elections. Although the woman was arrested in Bordesley Green, her husband is not standing in that ward.
Paul Tilsley, the Lib Dem group leader for the city council, said the party will assist the police and that it deprecates any misuse of the postal voting system.
'No touch' protocol
If anyone is found guilty of fraud they will be disciplined by the party as well as the courts, he said.
All the main parties on the council signed a "no touch" protocol in relation to postal votes which is beyond what is agreed by parties nationally.
Mr Tilsley said even if the allegations of fraud are unfounded, the incident does breach the protocol.
A West Midlands Police spokesman described the recovered items as "the element that has to be sent in" from postal voting forms.
Det Insp Simon Wallis, from the force's economic crime unit, said: "There are other persons yet to be spoken to in connection with this matter."
'Area for concern'
Steven Hughes, the returning officer for Birmingham City Council, said his department was working closely with police and that postal votes had been an area for concern in previous elections.
In July 2005 by-elections were held in the city following vote rigging in 2004's elections.
The representatives for Aston and Bordesley Green were forced to step down after the Electoral Commissioner found evidence of postal ballot abuse.
One councillor was later cleared, on appeal, of corrupt practices.
A subsequent election court hearing, found that the ballot-rigging which went on in the two wards "would have disgraced a banana-republic".
Election Commissioner Richard Mawrey, ruled that thousands of votes had been forged, stolen or otherwise tampered with.
This year, the council had issued 59,962 postal voting forms, 10,000 less than the 2004 figure.
In a separate case Scotland Yard said officers were looking at suspicious activities in seven London boroughs amid claims of vote-rigging.