Prime sponsor Sen. Jim Honeyford said the changes will simplify workers' compensation calculations and give some relief to businesses struggling with a 29 percent rate increase this year, and potential similar increases over the next two years.
Critics said the bill, ESSB 5378 , is incredibly complex, and will end up cutting benefits to injured workers.
"It hurts those who are already hurt," said Sen. Karen Keiser, D-Des Moines.
The bill passed 25 to 24. Locally, only Sen. Lisa Brown, D-Spokane, voted against it.