PORTLAND — Two Oregon teacher unions have gone back to court against political activist Bill Sizemore to accuse him again of racketeering, this time in the 2008 elections.

The legal battle between Sizemore and the unions dates to 2002 and a racketeering lawsuit the unions won against a Sizemore political action committee.

In the suit filed Thursday, the Oregon Education Association and American Federation of Teachers-Oregon name Sizemore and Nevada millionaire Loren Parks, a contributor to conservative causes.

The unions claim Sizemore and Parks conspired to set up a sham charitable organization to hide money used to gather signatures and promote four ballot measures in 2008, including measures on teacher merit pay and public employee unions.

The racketeering complaint asks for $18 million in damages, or about three times the amount the unions spent to defeat the ballot measures.

It also seeks to ensure that Parks does not use any charitable organizations to contribute money to political causes in Oregon, where he has spent millions over the years.

Sizemore, the author of dozens of initiatives since the 1990s, called the latest lawsuit frivolous.

“It’s aimed solely at keeping me from putting measures on the ballot,” Sizemore said.

A phone listing for Parks could not be found.

The new union lawsuit, filed in Multnomah County Circuit Court, alleges Sizemore lied under oath in court when he claimed to know almost nothing about the nonprofit American Tax Research Foundation in Nevada.

Multnomah County Circuit Judge Janice Wilson ruled Sizemore improperly took money from the foundation and briefly jailed Sizemore last December after holding him in contempt for violating a previous court order against using a charitable organization to raise money for political purposes.

Testimony and evidence at the contempt hearing indicated Sizemore was running the American Tax Research Foundation and that he controlled more than $1 million in contributions from Parks.

Greg Hartman, attorney for the Oregon Education Association, said a hearing is set for Dec. 21 on trying to resolve how much foundation money Sizemore must repay.

“If we don’t agree, then the judge will have to make that determination,” Hartman said.

Sizemore still owes about $3 million to the unions for the jury award against his political action committee in 2002. He was later found personally liable for the award.

In 1994, Sizemore successfully sponsored a measure to scale back public employee pensions by requiring them to pay part of their salaries toward their pensions. Courts later struck down the measure, but he began to get other initiatives on the ballot, including a 1996 cap on property taxes.

He lost a Republican bid for governor in 1998 and had been mostly sidelined from politics after the 2002 jury verdict but made a comeback in 2008 with five measures, all defeated by voters.

After the 2008 elections, a political action committee called Oregonians for Honest Elections filed a lawsuit in Marion County Circuit Court, claiming the unions made false statements about Sizemore related to the ballot measures he supported. That suit is still pending.