A public interest group has filed a complaint to the ethics commissioner against former environment and finance minister Robin Campbell, who now represents the Coal Association of Canada.

Progress Alberta, a non-profit advocacy group, filed the complaint Monday over concerns Campbell violated the Conflict of Interest Act by becoming a lobbyist within a year of being a minister.

Campbell served as finance minister in the previous Progressive Conservative government until he lost his seat in the last provincial election. In November he was hired as president of the Coal Association of Canada.

According to the act, a former minister cannot lobby government until a full year has passed since they held the post. If that's the case, then Campbell's cooling off period would expire in May, said executive director Duncan Kinney.

He said he became aware last week that the former West Yellowhead MLA may be violating the act.

"We think cooling off periods are there for a reason," he said.

"We don't want former cabinet ministers taking advantage of their privileged position as a public office holder in order to privately benefit," Kinney wrote in a blog post on Progress Alberta's website.

Kinney said the ethics commissioner has requested to meet with him about his complaint later this week.

Ethics commissioner Marguerite Trussler said she isn't legally allowed to disclose if she's investigating, or even if she has received the complaint.

In general terms, she said the wording of the Conflict of Interest Act can be murky, but the sentiment is simple.

"It basically says you cannot lobby for a year," Trussler said.

If the commissioner does investigate and finds Campbell acted against the rules, he could face fine of up to $50,000.

Campbell did not respond to CBC's request for an interview.