PORTLAND, Ore. -- A new poll from Portland-based Hoffman Research Group shows growing opposition for Measure 97 and a strong lead for Hillary Clinton in Oregon.

Measure 97, which would enact a corporate minimum tax on businesses with sales over $25 million, had a significant lead in a statewide poll as recently as early September. But opponents have since released a barrage of advertising criticizing the measure.

The Hoffman Research poll found 47 percent of likely voters oppose the measure, while only 41 percent support it. Twelve percent of likely voters remain undecided.

Pollster Tim Nashif said he wasn’t surprised to see support for Measure 97 fall off as voters start to hear more about the measure.

“The ‘no’ vote is getting their message out,” Nashif said.

Opponents to the measure have raised more than $10.6 million dollars, with most of it coming from large corporations that would be impacted by the tax. They have already spent millions on advertising.

The poll also found Hillary Clinton leading Donald Trump in Oregon. Among likely voters, 45 percent said they would vote for Clinton, compared to 33 percent for Trump.

Libertarian Gary Johnson was at 8 percent and Green Party candidate Jill Stein was at 3 percent.

The poll was conducted between Sept. 29 and Oct. 1, after the first presidential debate.

The Fiverthirtyeight pollster ratings show Hoffman Research as leaning slightly Republican, but Nashif said the presidential results in the poll demonstrate that he had a representative sample of Oregon voters.