Mulcair will address the media at 11:15 a.m. ET. CBCnews.ca will livestream his remarks.
"Prime Minister Harper must apologize to our veterans and then, to show he's sincere about the apology, he must fire his minister of veterans affairs, Julian Fantino," Mulcair said in an emailed statement.
Mulcair's comment is in response to a meeting between veterans and the minister that took place Tuesday night.
Veterans who were in Ottawa to lobby against the closing of their regional offices left a brief, emotional meeting with Fantino visibly frustrated and saying they were disrespected.
In a news conference, a group of veterans said their Tuesday meeting did not go well. Video from the meeting shows Fantino and veterans trading testy exchanges.
Fantino released a statement saying that he and the veterans had a "candid conversation" during a "roundtable" and that meeting with veterans is one of the most important parts of his job.