The Huffington Post reports an oil worker received the cartoon in the form of a sticker at a job site.
They shared the photo with another person related to the oil and gas industry who posted it on Facebook.
That user, Michelle Narang, said the "disgusting" cartoon "represents everything the oil and gas industry needs to fight against".
"I'm absolutely sickened that X-site Energy Services would think that the hard working men and women in the energy industry would condone this representation of a child."
She said she called Sparrow to complain and was told "she's not a child, she's 17".
"I don't care how much you disagree with the laments of a child — in Canada we don't rape women and girls to teach them a lesson," Narang said.
The image attracted widespread condemnation across social media (and in the lower house of Canada's Parliament), with many suggesting it could be classed as child pornography.
Thunberg took to Twitter herself, saying: "They are starting to get more and more desperate... This shows that we're winning."
While the age of consent for someone having sex with an adult in Alberta, where X-site is based, is as low as 14, child pornography is classified as any visual representation of a person under 18 engaged in a sexual activity.
The Royal Canadian Mounted Police (RCMP) determined the cartoon "does not meet the threshold of a criminal matter".
RCMP Superintendent Gerald Grobmeier told the Huffington Post that while people assumed it was the Swedish teenager, that wasn't enough to go on.
"There's a lot of assumptions on who that person is when they write the word 'Greta.' Unfortunately, with criminal cases you can't make assumptions, you need facts," Grobmeier said.
He added the police thought it was "inappropriate" but not illegal, a decision that was backed up by a criminology professor at the University of Montreal.
Alberta's culture minister denounced the illustration as "deplorable" and horrendous".
The Canadian House of Commons unanimously condemned the sticker on Friday afternoon.
The member who tabled the motion to do so described the cartoon as "encouraging a violent sexual assault on a young environmental activist".
