Green Party Leader Elizabeth May, excluded from Monday's foreign policy debate, turned to social media to hammer the Conservative government on its record, including its decision to pass controversial security legislation.

May used Twitter to reiterate her opposition to the bill as testy exchanges unfolded on stage at the Munk Debate in Toronto.

"We've heard it again tonight that the price of protecting our freedom is Bill C-51," May said in the online message.

"That the anti-terrorism act is somehow going to keep us safe and that those of us that are against it, are merely concerned about civil liberties and soft on terrorism, that's not true."

May said Bill C-51 makes Canada "both less free and less secure."

"We need to repeal Bill C-51," May said.

The legislation, which has caused friction between the NDP and the Liberals during the course of the election, became a topic of debate on Monday.

"The NDP took a very strong, principled, stand against Bill C-51. We looked at it, we knew it was wrong," Mulcair said, taking aim at Liberal Leader Justin Trudeau.

The Grits, who supported the bill in Parliament, have promised to amend Bill C-51 if they form government.

TPP targeted

May also used Twitter to criticized the Conservative government for moving ahead on the Trans Pacific Partnership.

The TPP is a massive trade pact that is being negotiated by 12 countries, including Canada, Australia, Brunei, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam.

The Conservative government hopes to have an agreement in place before the weekend.

Negotiations are currently underway in Atlanta.

"At this point, only the Green party opposes the TPP," May said.

"It includes threats to our supply management system, it includes a provision that ensures that Crown corporations have to be profitable, that certainly is a threat to CBC and it includes provisions favourable to global pharmaceutical industries that will increase the price of prescription drugs, just when need to decrease them."

She also took aim at Conservative Leader Stephen Harper on Canada-U.S. relations.

"Canada has been tone deaf to relationship issues with the United States," she said.

"We need to fix this."

Harper tried to defend his reputation during the debate, where he also faced criticism on this issue by the opposition leaders.

"We have a great relationship with the U.S. administration," he said.

"I have a great relationship with President Obama and, by the way, the Americans have never said otherwise and neither have we. This is just an invention."

The Green party leader has now been included in two debates and left out of two others.

She was invited to participate in the event held by Maclean's magazine and the first French language exchange hosted by Radio-Canada last week.

May was not asked to participate in Monday's exchange and she was left out of the Globe and Mail's economic debate in Calgary earlier this month.

When she was excluded, she became deft at using social media to offer her views on the topics under discussion.