Hoping to reinforce the differences between his Liberal Party and its chief electoral opposition, Prime Minister Paul Martin is warning that a Conservative government would undermine minority rights.

Speaking to reporters in Ottawa Monday, Martin offered a brief civics lesson in which he outlined his view of the role of the Charter of Rights.

"In a nation like Canada," Martin explained, "we have got to ensure that minority rights are protected when challenged by the majority. And the only way in which you can do this is to have a Charter, which is ultimately interpreted by the Supreme Court of Canada."

According to Martin, Conservative Party Leader Stephen Harper has indicated he thinks differently.

Harper's recent suggestions that a Conservative government might consider invoking the Charter-overriding notwithstanding clause, Martin said, point to a "fundamental difference" between the two leaders.

"I would not use the notwithstanding clause," Martin said. "And if what you're prepared to do is use the notwithstanding clause, then what you're saying essentially is minority rights can be subjected to the will of the majority.

"I've got to tell you that is not the kind of country I believe in, nor do I think it's the kind of country that Canadians believe in."

When Justice Minister Irwin Cotler spoke to reporters hours later, he too expressed concern that the Canadian model of constitutional democracy would be threatened. The Conservative Leader, Cotler said, would undermine the "rights revolution" spurred by the Charter, while intruding on the independence of the judiciary.

In his comments Monday, Martin also tried to squash suggestions his own party is divided on the issue of abortion.

"Never, never will I allow the rights of women to be removed by going back to the past," Martin said in French. "I believe that the situation in Canada is a free choice for women. They have to decide for themselves."

The Charter has the final say on such matters of "fundamental rights," Martin said, explaining that for that reason, he would not allow such matters to be put to a free vote.

"Never, never will I allow the rights of women to be trampled on by legislation in that area."

And Martin also touched on another issue he has been trying to use a wedge between the Liberals and Conservatives.

Despite his pre-election decision to keep same-sex marriage off the election agenda by amending the questions referred to the Supreme Court, Martin is now a firm advocate of the unions.

When reporters asked the prime minister what he would do about the members of his cabinet who voted against same-sex marriage in Parliament last fall, Martin said that sometimes MPs can make mistakes.

"That's precisely the purpose of the Charter," Martin said, again describing the courts' ability to check when the "will of the majority has been misplaced."

Reporting from CTV's roving Election Express, Craig Oliver said the Liberal strategy -- coming hot on the heels of the Conservatives' quiet election platform release -- could throw a wrench in the Conservatives' so far trouble-free campaign.

"All of this is now coming to the fore at a time when Canadians haven't been paying much attention to what voting for the Conservatives represents," Oliver said from Smiths Falls, Ontario.

"And the Liberals are hoping they'll now start doing that."