One of the advocacy groups prominently backing Commissioner Steve Novick and Mayor Charlie Hales' controversial bid for millions in new transportation revenue has just issued a soft ultimatum concerning that support—given the likelihood that certain business interests have promised to put the plan before voters next spring.

Ditch the more spread out income tax that's been cooked into the "Portland Street Fund" proposal as drafted—a concession that failed to win support from the Portland Business Alliance despite months of talks and negotiations—and replace it with a tax that's far more progressive.

That demand comes from OPAL Environmental Justice Oregon, in the form of a letter (pdf) from its executive director, Jonathan Ostar. He's almost certainly referring to a proposal, floated in a poll this summer, that would have raised up to $55 million just by taxing Portlanders making $125,000 a year or more. A very eye-opening 60 percent of respondents said they liked that idea.

OPAL's letter also seems to be asking Hales and Novick to undo another concession handed the PBA: tilting the balance of spending from the "Street Fund" back toward safety and away from maintenance.

Should a proposal eventually be referred to voters, OPAL's willingness to join the "Yes" campaign and invest resources in upholding this proposal will likely depend on whether the City Council passes a truly progressive package, one that is fairer for the middle class and places a stronger emphasis on safety. Given our unwavering support, and given that the concessions afforded to the business community have not secured the level of support intended, we recommend that City Council amend the proposal to ensure that working families and middle-class households are not burdened at the expense of the wealthiest among us, who can clearly afford to pay more.

Ostar has already told me he sees the PBA's opposition as "a stab in the back." I quoted him saying so in Hall Monitor, out today, which also suggested that Hales and Novick revert to the more progressive, and apparently more popular, tax plan floated this summer.

A ballot fight—if it's framed around rich Portlanders' distaste for an income tax that helps poor people—might actually turn out okay for Hales and Novick.

Unlike in 2008, Portland's not in a recession. We approved another local income tax, the $35 arts tax, in 2012. The city also went big for 2010's Measures 66 and 67, which raised income taxes statewide in defiance of the business community's sorrowful wails.

"City hall starts with an advantage," says Tim Hibbitts, a partner at respected local polling firm DHM Research—that is, assuming opponents don't successfully frame a campaign around waste and mismanagement instead.

"It's a liberal city," Hibbitts says. "It's not averse to taxes."