It's about enshrining all tax breaks that currently exist in Oregon in the state's constitution.

Currently, state law requires that no new taxes be imposed without approval by a three-fifths majority of both legislative chambers. Measure 104 would amend the constitution to apply the three-fifths requirement to include any attempt to legislatively raise revenue by boosting fees or reducing or killing existing tax breaks.

The primary supporters of Measure 104 are the Oregon Association of Realtors. The association's specific goal is to protect the mortgage interest deduction, which allows homeowners to deduct interest they pay on home loans from their taxable income (most states that collect income taxes allow such a deduction; 10 do not).

There are a number of reasons 104 is on the ballot: Democrats are indeed looking at killing or reducing existing exemptions.

A 2017 bill that would have ended the deductibility of second home mortgages died without a vote. But some Democrats have pledged to go after both first and second home mortgages. Second, the Oregon Supreme Court ruled in 2015 that lawmakers could indeed eliminate tax exemptions with a simple majority vote. That ruling was contrary to prior guidance from legislative counsel. Finally, Republicans fear new fees could emerge from climate policies, like cap and trade.

Measure 104 would do more than protect the mortgage interest deduction, however. It would also limit lawmakers' authority to raise fees or reduce tax breaks.

Paul Rainey, a spokesman for the Yes on 104 campaign, says that's a good idea.

"We think Oregonians want to keep Kate Brown and others' hands out of the cookie jar," he says. "Right now, it's too easy to raise revenue without a three-fifths vote."

Measure 104 would protect 367 exemptions, loopholes and tax breaks that collectively cost the state more than $12 billion a year—more than the entire sum of personal income taxes the state collects annually. The largest of them are largely uncontroversial, like the deductibility of employer's health care coverage and pension contributions. Some of the smaller ones, like the exemption on your boat and for Hollywood film and television productions, have their own critics—and defenders.

"There is already an army of lobbyists looking to protect the status quo," says Juan Carlos Ordóñez of the left-leaning Oregon Center for Public Policy. "This measure would make their jobs a lot easier."