Federal Green Leader Elizabeth May and NDP MP Kennedy Stewart have been charged with criminal contempt of court for their part in an anti-pipeline protest in B.C. earlier this year.

Special prosecutors approved charges against the politicians after reviewing the evidence gathered in each of their cases, the B.C. Prosecution Service announced Monday.

Stewart, who recently announced he intends to step down as MP so he can run for Vancouver mayor, pleaded guilty to his charge the same morning and was handed a $500 fine.

A spokesperson for Stewart said the charge is non-indictable, and won't affect his ability to run for mayor.

Both he and May were arrested on March 23 outside one of Kinder Morgan's two Burnaby terminals, which are both protected by a court injunction requiring protesters to keep at least five metres away.

About 200 other anti-pipeline protesters have been arrested in recent months.

Some have already been criminally charged, but special prosecutors were brought in to handle May and Stewart's cases to "avoid any significant potential for real or perceived improper influence in the administration of justice," the B.C. Prosecution Service said.

May and Stewart, who are both outspoken pipeline critics, were defiant at the time of their arrests, and said they knew they risked legal trouble for taking part in the demonstration.

"The commitment to build a pipeline in 2018 when we're in climate crisis is a crime against future generations and I will not be part of it," May told reporters as she was being taken away.

She hasn't commented on the special prosecutors' decision, and it's unclear whether she will be fighting the charge.