The agency says it acting on a complaint from a Progressive Conservative member of the legislature, Tim Houston, alleging the Liberal caucus sent out postcard-style flyers paid for by the province.
The byelections haven't been called yet but the provincial law says the rules prohibiting partisan advertising apply when a seat becomes vacant.
Houston alleges the Liberals violated Section 272 of the Elections Act, which says: "No person shall knowingly conduct election advertising or cause it to be conducted using a means of transmission of the government of the province."
He also says the flyers sent out to residents in the constituencies of Sydney-Whitney Pier, Cape Breton Centre and Dartmouth South are an attempt by the Liberals to gain an advantage in the expected byelections.
In a separate letter to the Speaker of the legislature, Houston also argues the Liberals have violated the "spirit and the letter" of the legislature's rules on mailouts and he asks that the party reimburse the public.
Andrew Younger, a Liberal member of the legislature, said the party doesn't think it has done anything wrong and other parties have sent out party caucus flyers when seats are vacant but elections or byelections haven't been called.
"We have lots of examples of past practice where Elections Nova Scotia ... in very similar circumstances have said sending out flyers into an unheld riding is perfectly fine," he said.
If Elections Nova Scotia determines the practice is not permitted, he said his party will comply with the ruling.
Dana Doiron of Elections Nova Scotia says the agency will make a ruling in a matter of days on whether the mailout violates the law.