An attorney for Multnomah County has weighed into the fight over an Oregon ballot measure that would enshrine a ban on "grocery" taxes in the state constitution.

There's little doubt that Measure 103 would prohibit the soda tax that has been contemplated by the county for years.

But the legal opinion says the measure would have wider impacts. According to the county attorney, the measure would cut into Multnomah County's ability to collect existing taxes—and 40 percent of the taxes received by the county's general fund could be affected.

That's because there's ongoing debate about the extent to which fuel and other taxes would be subjected to the exceptions. The county attorney says it's all but impossible to come up with a dollar figure for the impact on the county.

"We may reasonably conclude that it would affect collections from the County's motor vehicle fuel and rental taxes and business income tax," writes Will Glasson, Assistant County Attorney, in an opinion dated Sept. 20.

"Measure 103 would impose significant challenges on the county's ability to collect different assessments and to administer 'grocery'-proximate operations," the opinion says. "However, estimating the actual fiscal impact of Measure 103 is functionally impossible, at this point, due to the new and unprecedented administrative challenges that the amendment would create."

County Commissioner Jessica Vega Pederson, who opposes Measure 103, says "there are significant potential financial impacts. The potential administration [is] problematic."

Backers of the measure say the county analysis is an error, because the tax is limited to groceries.

"It's only on food for human consumption," says Joe Gilliam, spokesman on Yes Keep Our Groceries Tax Free.