Metro is exploring a payroll tax to fund the regional government's proposed 2020 transportation measure.

Metro officials estimate they may need $350 million to $450 million a year to finance bonds.

"All the revenue sources Metro can legally raise are under examination," says Andy Shaw, Metro's government affairs director, though he adds no decisions have been made.

Related: People are already arguing over where the massive measure should be spent.

Metro President Lynn Peterson updated the Portland Business Alliance last week on ways Metro could raise the money, including a payroll tax. PBA opposed such a tax when Portland State University proposed one in 2016.

"No assumption should be made that we're taking a position one way or another right now," says alliance spokeswoman Amy Lewin. "We have been supportive of the process to explore transportation investment."