Sean Kilpatrick/CP Green Party Leader Elizabeth May asks a question in the House of Commons on Oct. 3, 2016.

"Nothing was more painful than watching the destruction of our environmental laws in 2012," she said.

Green Party Leader Elizabeth May rose in question period Monday to talk about the worst thing she's experienced since becoming an MP six years ago.

In June that year, May stayed in the House of Commons for almost 24 straight hours to vote against the then-Conservative government's omnibus budget bill and its sweeping changes to environmental regulations.

She was one of just five MPs to be present for all 157 votes, according to Maclean's, and drank enough water to stay hydrated without having to leave for the bathroom. She cried as MPs cheered once she cast her final vote.

Tories used another piece of omnibus legislation that fall to remove thousands of lakes and streams from federal protection under that law, at the apparent urging of the pipeline industry.

Green leader presses Liberals on promises

But on Monday, May noted that Liberals promised to reverse those changes. She pointed to a line in the mandate letter given to Transport Minister Marc Garneau to "review the previous government's changes to the Navigable Waters Protection Act and restore lost protections."

"But now it appears increasingly clear that's not the plan," May said, before asking Garneau if she had that wrong.

Garneau said he wanted to "reassure" May that he takes his job seriously. And he attempted to salute her voting marathon five years ago.

"I remember spending all night long with my honourable colleague..." Garneau began.

The remark immediately sparked guffaws and catcalls.

"... when the previous government gutted the Navigation Protection Act," Garneau powered through.

He pledged that Liberals would go beyond recovering many of the things scrapped by the last government.

Twenty-four hours. Twenty-four hours of non-stop voting was a principled stand and should not be the source of schoolyard bullying.Elizabeth May

"I would encourage members to be careful in their wording," House Speaker Geoff Regan added for good measure, spurring more chuckles.

But May — whose pleas for decorum in the House sometimes win her applause and other times eyerolls — did not find it all so funny.

"I would like to thank the honourable minister of transportation and ask for some maturity from some members in this place," she said.

"Twenty-four hours. Twenty-four hours of non-stop voting was a principled stand and should not be the source of schoolyard bullying."

And with that she quietly sat down in her little place in the corner of the House.