Canada’s chief electoral officer is still looking into the “complex” matter of mass mailing campaigns carried out by MPs, according to a letter obtained by CBC News.

The letter from Marc Mayrand to House of Commons Speaker Andrew Scheer and the Board of Internal Economy says, “I understand that the Board is concerned with the use of Members of Parliament resources for partisan purposes.”

It is the second time Mayrand has responded to the Speaker and the Board in reference to specific complaints about mass mailings sent out by the NDP that are deemed overly partisan.

On Tuesday, the Speaker ruled the NDP had broken the rules, saying the letters were meant “for the benefit of the NDP as a political party and to advance electoral purposes." The board is now looking into “remedies.”

Scheer had previously asked Mayrand to look into about 385 000 mailings using House of Commons resources sent to three ridings in a byelection last year.

Elections Canada cleared the NDP of any wrongdoing in that because none of the letters was sent during the campaign period.

However, Scheer wrote again to point out a total of almost 1.8-million letters sent out by the NDP using MP mailing privileges between July 2013 and January 2014.

He asks whether, because of the partisan content of the letters, they constitute a “donation-in-kind” to the NDP from the House of Commons.

In his response, Mayrand says he is already in touch with the law clerk of the House of Commons about this.

“These are complex matters that warrant careful consideration.”

Mayrand writes it is important that his office continue to work with the law clerk, “in order to be able to provide clear guidance to Members of Parliament regarding the use of House of Commons resources, especially as we approach the next general election.”