Mya Chau and Eve Helman don’t drink coffee, but they know that for many Canadians, swinging by Starbucks to grab a morning joe to go is practically a reflex. They also know that most of those white and green coffee cups get tossed in the trash, unable to be recycled with regular paper because of their plastic lining. The Calgary 6th-graders can tell you that more than a million trees are cut down each year to make the 1.4 billion Starbucks cups that are used once and then sent to landfills in Canada alone. And they want that to change.

On Wednesday, 12-year-old Chau and 11-year-old Helman will join several environmental groups, including Stand.earth and Greenpeace, in Seattle, where they hope to attend Starbucks’ annual shareholders meeting and present CEO Kevin Johnson with a petition—signed by 230,000 people and counting—asking his company to commit to making a fully recyclable cup.

“We want them to make a tree-free cup that can be recycled everywhere,” says Chau. “We know they can be a leader since Starbucks is in the whole world.”

Chau and Helman, who are classmates at Terrace Road School, first became aware of the problem of disposable coffee cups two years ago after hearing their parents discuss it. For a science fair project, they decided to survey people about their coffee drinking habits to get a sense of how many cups were being discarded locally. The pair interviewed 157 people and found that on average, each person throws away 155 cups per year, all of which end up in the landfill.

This year, they decided to take their project further by starting a petition on Change.org. Their goal was to get 900 signatures, but the petition blew up on social media, getting hundreds of shares—including a retweet from author Margaret Atwood—and quickly racked up more than 100,000 signatures.

“We just did it so that more people would be aware of the cause,” says Helman. “Now that we got this far, we feel so proud of ourselves.”

Starbucks’ shareholders are expected to vote Wednesday on a sustainability proposal put forward by advocacy group As You Sow that asks the company to recommit to a pledge made in 2008 to develop a fully recyclable cup and ensure that a quarter of its beverages are served in reusable containers. The board of directors has recommended that shareholders vote against the proposal on the grounds that Starbucks has promoted and incentivized the use of reusable cups by offering discounts when customers bring their own mug, and has introduced recyclable sleeves and lids for its disposable cups.

Gina Ko, Chau’s mother, says it’s not clear whether the girls will be able to personally deliver their petition. But Dawnelle Frew, Helman’s mother, says they’re proud of their daughters either way.

“To have such passion when really, it’s adults that are making the mess, is amazing,” she says. “Whatever happens on Wednesday, this is going to make a difference in their lives.”