Multnomah County Commissioner Sharon Meieran and Rep. Rob Nosse demonstrate how to canvass for signatures for a soda tax initiative on the May 2018 ballot. Ericka Cruz Guevarra / OPB

Holding a clipboard, Rep. Rob Nosse practiced a few knocks at his fictional front door. He was demonstrating to a group of volunteer canvassers how to approach Multnomah County voters about signing a petition to get the soda tax on the May 2018 ballot.

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"I try to use a friendly knock," Nosse told the crowd. "Something that doesn't sound law enforcement-type. Something that seems friendly and inviting."

On Saturday, canvassers began the work of gathering the 18,000 signatures needed to secure a spot on the ballot for a soda tax initiative that would add 1.5 cents per ounce, or about 18 cents to the cost of a 12-ounce can of soda, energy drink or sweet tea.

"We are facing an epidemic of sugar-related diseases that put the lives and the futures of our kids at risk," said Multnomah County Commissioner Sharon Meieran, who is also an emergency room doctor. "Here in Multnomah County we have the opportunity to help kids grow up healthy and strong to reduce the consumption of sugar where it's having the worst impact on kids, and that is soda and other sugary drinks."

If canvassers succeed, and if the initiative is approved by voters, Multnomah County would be the first in the state to win a soda tax fight that, for years, was an uphill battle against deep-pocketed beverage companies.

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"As we know, taxation statewide doesn't always get the best momentum for conversations, which is why we believe passing it at the local level will set a good example for other counties and other jurisdictions to consider doing the same," said Cyreena Boston Ashby, chief executive officer of the Oregon Public Health Institute.

Opponents of the soda tax are concerned about the possibility of a successful soda tax campaign in Multnomah County, and what that could mean for a state that has yet to see what a successful soda tax campaign looks like.

Related: Would A Soda Tax Work In Multnomah County?

"We at this time have no mechanism for collecting a tax of this nature, so developing a tax for a particular kind of product will essentially create a new bureaucracy," said Felicia Heaton, a spokesperson for the Move Forward Multnomah Coalition, an anti-soda tax group. "We're not necessarily prepared to handle that in Oregon, in Multnomah County."

Proponents of the tax say it would raise millions of dollars for local pre-schools, physical activity and nutrition initiatives. The "Yes! For Healthy Kids and Education" campaign is backed by a coalition comprised of the American Heart Association, the Oregon Public Health Association and the Oregon Public Health Institute, among others.

Opponents are riding the wave of the affordability debate in Portland.

"It's already skyrocketing to pay the rent, to be able to afford to buy a home in Portland and throughout Multnomah County," Heaton said. "This is just one more thing that adds to the struggle of that process."

Several cities have passed similar sugary drink taxes. Berkeley, California, was the first and consumption there dropped 20 percent over two years.

Successful or not, the canvassing efforts that began Saturday give a look into what arguments both sides of the soda tax debate will make when the election draws near in Oregon's most populous county.