A testy exchange between Conservative Leader Stephen Harper and Liberal Leader Justin Trudeau over the revocation of citizenship was one of the most talked-about moments after Monday night's leaders' debate on foreign policy.

The debate came to a boil when Harper asked Trudeau, "Why would we not revoke the citizenship of people convicted of terrorist offences against this country?"

"A Canadian is a Canadian is a Canadian," Trudeau responded. "And you devalue the citizenship of every Canadian in this place and in this country when you break down and make it conditional for anybody."

NDP Leader Tom Mulcair has said that the revocation of citizenship would create two levels of citizenship. 

The NDP and Liberals have both said they would repeal Bill C-24 if elected on Oct. 19.

Bill C-24 is the legislation responsible for the changes to the Citizenship Act, which included the revocation of citizenship, a provision that came into effect in May.

The changes to the act are currently being challenged in court by a coalition of civil liberties groups.

The leaders' debate has raised several questions about what the government is allowed to do.

Here are five things to know about the revocation of citizenship:

1. Terrorism-related offences

The government can revoke the citizenship of dual nationals — that is, of Canadians who hold a second citizenship â€” and who have been convicted of high treason, terrorism, engaging in an armed conflict against Canada and other terrorism-related offences with respect to matters of national security. 

Under the newly revamped act, the government can strip the citizenship of dual nationals, but not if it renders them stateless. The onus appears to be on the person who is having their citizenship revoked to prove that they are not a dual national.

Citizenship can also be taken away from a person who is found to have obtained it fraudulently.

2. Convictions in a foreign court

Revocation of citizenship requires a terrorism-related conviction, but not necessarily from a Canadian court.

A foreign court could convict a Canadian citizen of a terrorism-related offence, which could be enough for Ottawa to strip someone of citizenship.

That decision is left at the discretion of the immigration minister.

3. Immigration minister has final say

Before revoking a person's citizenship, the government must provide the person with a written notice and give them a certain number of days to respond.

The person whose citizenship is being revoked only has the right to respond in writing.

There is no court hearing unless the minister of immigration decides one is required.

4. Foreign fighters

Under the recently revamped Citizenship Act, the immigration minister has the final say in decisions to revoke citizenship.

Only complex cases such as "war crimes, crimes against humanity, security, and other human or international rights violations" will be decided by the Federal Court.

Wesley Wark, a national security affairs and terrorism expert with the Graduate School of Public and International Affairs at the University of Ottawa told CBC's The Current on Tuesday that a Federal Court would also rule in cases where the government wants to revoke the citizenship of a person convicted of serving as a member of an armed force or group that was engaged in an armed conflict with Canada.

5. Exporting terrorists abroad?

Zakaria Amara passport

Zakaria Amara, convicted in the Toronto 18 bomb plot, is a dual citizen of Jordan and Canada. He has been told his citizenship will be revoked. (Associated Press/Reuters)

The federal government has sent revocation letters to at least five people linked to extremist activity, including Zakaria Amara, the man serving a life sentence in connection with the Toronto 18 bomb plot.

He is a dual citizen of Jordan, where the Canadian government will deport him once the revocation is final.

During an interview with CBC News Network's Power & Politics on Tuesday, Conservative MP Parm Gill was pressed on the dangers of deporting a convicted terrorist such as Amara abroad.

"Our first and primary responsibility is the safety and security of Canadians," Gill told CBC host Rosemary Barton.

Gill rejected the suggestion that Canada would be exporting terrorism abroad, saying, "If we have the option of fighting them over there, while they're there, we'd much rather do that rather than bring them in our country and fight them here at our land.

"If someone holds a dual citizenship and is convicted of a serious terrorism charge or carries weapons against the Canadian Armed Forces, they don't deserve to be in our country and they will be deported, assuming they hold a dual citizenship."