Chief electoral officer Marc Mayrand says as long as the flyers were mailed before the byelections were called — as NDP Leader Tom Mulcair insists they were — they do not constitute an election expense.
Mulcair has acknowledged some flyers arrived in mailboxes after the byelections had been called.
Conservatives and Liberals had accused the NDP of improperly using taxpayer-funded parliamentary resources for partisan purposes.
The all-party board of internal economy, which oversees the financial affairs of the House of Commons, last week asked Elections Canada to determine whether the flyers constituted a campaign expense which may have pushed the NDP over its spending limit for the byelections.
The board may yet review the rules for bulk mailings by MPs into ridings where byelections are imminent.
At issue were flyers sent by various New Democrat MPs into Toronto Centre, the Montreal riding of Bourassa and the Manitoba riding of Provencher.
The Conservatives have also complained of similar flyers arriving in a fourth riding, Manitoba's Brandon-Souris, where a byelection was held at the same time.
Mayrand responded to the internal economy board's request in a letter to Commons Speaker Andrew Scheer, who chairs the board.
"In the case of mailings sent by a member of Parliament, Elections Canada's long-standing position is that when a mailing is issued prior to the writ, or when the mailing is in transit when the election is called and the member is unable to stop the delivery, the mailing is not a regulated expense," Mayrand said.