After two years with a tied House of Representatives, Oregon voters could flip control of the chamber to one party in Tuesday's election.
The Senate also is up for grabs.
About a dozen competitive districts, most in the Portland suburbs, will determine which party takes control - if one does. Another tie is possible in the House and Senate.
A report of vote tampering by a Clackamas County election worker in the eastern Portland suburbs had the potential to impact the outcome of some key races and partisan control of the Legislature, if the results are close and there are a significant number of compromised ballots.
Investigators and election officials have not said how extensive the tampering might have been, beyond a report from a county lawyer that two ballots are highly suspect.
The party that controls a legislative chamber has the power to set the agenda in Salem for the next two years and to block or advance the priorities of the Democratic governor.
All 60 House seats and 15 of the 30 Senate seats are on the ballot. The winners will have to contend with a sluggish economy and costs that are growing faster than revenue.
Republicans have promised to roll back pension benefits for public employees and create jobs through tax changes and promoting development of natural resources. Democrats have said they'll promote jobs by funding infrastructure improvements and job training.
Despite years of tough budget cuts, there will almost certainly be more trimming as the economy recovers slowly and costs rise faster than state revenue. Decisions about what to keep and what to protect will only get harder.
At the same time, state and local governments will have to sharply increase their employee retirement contributions to make up for a steep shortfall in state pension funds.
Republicans have demanded significant changes to public pension benefits, although state Supreme Court decisions severely limit the options available.
Democrats, who often benefit from large contributions from public employee unions, have historically resisted changes to the Public Employees Retirement System.
Gov. John Kitzhaber has convened meetings with unions and business leaders to discuss wholesale changes to the state tax system. Another Kitzhaber panel is studying changes to sentencing laws.
Both initiatives could fizzle or result in politically perilous votes for the Legislature.