Three mothers who lost their children to impaired drivers were invited to sit in the House of Commons gallery for the tabling of the new bill.
Those three women are behind a Families for Justice Petition that has gathered more than 90,000 signatures.
The petition calls for a five-year minimum mandatory sentence for anyone convicted of impaired driving causing death.
Asked Monday about the legislation on CBC's Power and Politics, MacKay would not give details. He said the proposed law is intended to "send the message that those who are causing this carnage on the highways, who take that risk, will face severe penalities."
MacKay said drunk driving remains the number one criminal cause of death in Canada.
Legislation passing will have to wait
With the session set to end next week, the new legislation will not pass before Parliament rises for the summer.
MacKay called it "placeholder" legislation for future governments to consider after the next federal election, expected to be called this fall.
Sheri Arsenault of Beaumont, Alta., was among those invited to be in the Commons Tuesday. She lost her 18-year-old son, Bradley, in a horrific crash in November 2011. Two of his friends were also killed in the collision.
Jonathan Pratt was convicted of three counts of manslaughter and impaired driving causing death. He was given an eight-year sentence and a lifetime driving prohibition.
Arsenault has met with MacKay in the past to advocate for stiffer penalties.
"You know, it's time that this is recognized as a serious crime and alcohol cannot become the excuse," she said.
The current maximum sentence for drunk driving causing death is life imprisonment. There is no mandatory minimum sentence.