SALEM — Millions of dollars have been raised by the two groups campaigning on opposite sides of a November ballot measure that would increase corporate taxes.

Measure 97 would create a 2.5 percent tax on sales exceeding $25 million for some corporations. Last week Gov. Kate Brown endorsed the measure, which would be the largest tax hike on corporations in Oregon history.

The Statesman Journal reported that Our Oregon, the group supporting the tax, has raised $1.5 million so far. The money is from just two donations of $750,000 each by the Oregon Education Association and SEIU Local 503, the state’s largest public sector unions.

The business-backed Defeat the Tax on Oregon Sales is campaigning against Measure 97, and has raised more than $5 million from nearly 800 donations. Most contributions are from corporations or their executives.

The campaigns are likely to spend heavily on television, radio and digital advertising.

Supporters of the measure say it would reignite investment in public schools, health care and senior services, all while allowing the state to tackle its other financial problems. Opponents say it would hurt businesses and curb private sector growth.

Other officials have said Measure 97 could help avert a looming $1.4 billion budget deficit. The potential deficit is being driven by the cost of implementing the Affordable Care Act — also known as Obamacare — public pension costs and a higher demand for state services, among other reasons, officials said.

A report from the nonpartisan Legislative Revenue Office found the measure would raise $3 billion a year, but act as a regressive tax by increasing prices. The higher prices amount to an average per capita tax increase of $600 a year, mostly affecting low- and middle-income Oregonians, the report showed. The report also found that Measure 97 would slow private sector job growth while boosting public hiring.

The extra funds that would be generated by the measure are broadly earmarked for education, health care and senior services, although it doesn’t say how the money should be spent in those areas. However the Legislature could spend the new funds anyway it pleased.

Brown, a Democrat who’s running to keep her gubernatorial seat in November, addressed this issue in her endorsement, saying she “will make sure” the funds are spent as voters expect.