Official sources said an election team spotted Lyngdoh using an official vehicle while campaigning for his party candidate R P Rani on Friday last.
HSPDP is presently a partner of the Congress-led Meghalaya United Alliance (MUA) government and Lyngdoh is the Chairman of state Administrative Reforms Commission.
The state election department, which had videographed the entire campaign, filed a case against Lyngdoh with the police under section 188 IPC for violating the election code of conduct.
Chief Electoral Officer (CEO) Prashant Naik said his office will go through the official report before apprising the Election Commission.
The by-election to Laitumkhrah was necessitated after former United Democratic Party (UDP) MLA Ampareen Lyngdoh quit from the assembly to join Congress.