Thousands of people attended an annual anti-abortion rally on Parliament Hill Thursday afternoon, with many of them calling on Prime Minister Stephen Harper to reopen the abortion debate.

When the abortion issue came up during the recent federal election campaign, Harper promised not to reopen the debate and said any legislation brought forward seeking to do so would be defeated.

But organizers of Thursday's event are counting on Harper, particularly now that he has a majority government, to backtrack on his promise.

"Hopefully there will be a change of heart," Matthew Wojciechowski, a member of Campaign Life Coalition, said at a news conference held before the rally.

Members of Parliament have tried before to make abortion-related changes to Canada's laws by introducing private member's bills. Most recently, Conservative MP Rod Bruinooge tried to make coercing a woman to have an abortion a criminal offence, but his bill was defeated.

Wojciechowski said his organization would continue to encourage MPs to introduce those kinds of bills.

"We hope that those who have been active in the past will continue to be active in the future," he said.

A handful of MPs attended the rally and addressed the crowd, which police estimated at about 5,000 people. Scott Reid, Royal Galipeau, Stephen Woodworth and David Sweet, all from the Conservative caucus, made brief comments. They were introduced by a former Liberal MP, Pat O'Brien, who said normally there are more than 20 MPs who show their support for the cause at the yearly event, but they were missing Thursday because of the recent election and Parliament not currently sitting.

O'Brien and other rally organizers say the anti-abortion movement is gaining strength in Canada and that Harper should listen to Canadians who want the debate reopened.

"Although the prime minister has said he's not interested in opening the debate, well newsflash prime minister, the debate is on. These people say so," O'Brien said, gesturing to the large crowd. He left the Liberal party to sit as an Independent MP because of his opposition to same-sex marriage legislation.

Also among those gathered on Parliament Hill on Thursday was a group of pro-choice advocates.