PORTLAND, Ore. (AP) -- A ballot measure that aims to tie teachers' pay to their "classroom performance" is adding another round to a long-running feud between the state's teachers unions and conservative activist Bill Sizemore.

Sizemore, a one-time gubernatorial candidate who sponsored the teachers' pay initiative and four others on the November ballot, says basing educators' salaries on merit rather than seniority would improve the quality of the state's schools.

Opponents argue otherwise. Members of Parents and Teachers Know Better, a coalition of teachers unions, parent and education organizations campaigning against the measure, say that if passed the measure would lead to more standardized testing, forcing educators to "teach to the test" instead of work with individual students.

"I think one of the problems with merit pay is how you determine merit," said Larry Wolf, president of the Oregon Education Association. "We really like to look at the whole student."

He added that establishing a merit pay program would likely cost taxpayers more because the state would have to establish the framework to measure classroom performance.

"When Oregon voters look at those kind of issues they tend to say no to Bill," Wolf said.

In 2000, a similar measure proposing to tie teacher's pay to students' test scores was on the ballot. Voters rejected it by nearly two to one.

Since then, merit pay plans with varied guidelines have been set up in other states and school districts, such as Minnesota and Denver.

With more national attention placed on merit pay programs, Sizemore said, Oregon voters may be more likely to pass the initiative.

He added that unlike 2000, this year's measure does not specifically tie teacher pay to student test scores, though Sizemore says that would be one option if Oregonians vote to pass it.

"It's a possibility," he said. "It's just as possible it wouldn't include any testing."

Sizemore said teachers' performance could also be based on evaluations or demonstrated student improvement.

"I'm not so interested in how we measure classroom performance," he said. "It's that the current system is a dismal failure."

State and local school boards should decide how to carry out the measure, he said.

The state has not yet determined who would enforce the measure if it becomes law, said Morgan Allen, legislative director for the Oregon Department of Education.

"It gives no direction," he said. "It's full of unintended consequences."

Opponents of the measure call its language "vague and poorly worded."

Six years ago, a jury awarded $2.5 million to OEA and American Federation of Teachers-Oregon, two of the state's largest teachers' unions, in a fraud and racketeering lawsuit they brought against Oregon Taxpayers United, an organization founded by Sizemore.

The unions had claimed Sizemore used forgery and fraud to qualify two anti-union ballot measures in 2000.