Police are investigating allegations of vote rigging during the recent local elections in Oldham.
Greater Manchester Police said it was looking into claims that about 300 postal vote forms were sent to just four houses in the town.
The addresses are allegedly linked to relatives or supporters of a Liberal Democrat candidate.
The local Liberal Democrat party lost control of the council in the elections.
It said on Sunday that it had done nothing illegal or improper.
Election agent Keith Pendlebury said: "We have nothing to hide whatsoever."
But he added that the system of postal voting was open to "misuse and abuse" and needed looking into.
The allegations follow similar claims in 2001 when both the Liberal Democrats and Labour accused each other of ballot fixing in the town.