Fifteen business, labor and environmental organizations announced the challenge on Tuesday, invoking a 2005 law that requires signature-gatherers to personally sign a declaration that the information on the petition is correct.

Initiative 917 solicitors did not sign the statement on more than 3,000 of the 17,000 petitions, and those pages must be thrown out, the group said.

"The Legislature passed a law to ensure that signature-gatherers are honest and accountable," said Steve Mullin, president of the Washington Roundtable, the organization of top corporate CEOs. "There has been substantial fraud in other states, and laws like this are necessary to keeping the initiative process clean and to protect the voters."

The new law requires that petitions include a signed declaration on every sheet.

The state elections division initially planned to reject all pages without the solicitor's signature, but later deferred to an opinion by the attorney general's office that the signature was not absolutely required.

The challengers said the lawsuit apparently would affect only Eyman's initiative. Three other measures, dealing with the estate tax, alternative energy and property rights, already have been certified to the fall ballot.

A random sample failed to show enough signatures to secure a ballot spot for Eyman's measure, and the secretary of state's office is now checking an estimated 300,000 signatures. If the 3,000 pages were eliminated, it would disqualify I-917, since his campaign was already on the bubble.

The challengers said the state needs a clear ruling, both for Eyman's measure and for all future initiatives.

Eyman called it a "don't-let-the-people-vote" lawsuit.

"We consistently followed the evolving policies of the secretary of state regarding signature collection for Initiative 917," Eyman said in an e-mail to reporters. "Whatever they said to do, we did it."

He said challengers are so afraid of the measure passing, "they're desperately trying to impede democracy and stop the voters from having the chance to vote on it."

I-917 would repeal weight fees and other taxes passed by the 2005 Legislature as part of an $8.5 billion transportation package, as well as some local taxes, such as the Sound Transit regional vehicle tax. Eyman's measure would remove an estimated $2.7 billion from state projects and revamp the way government calculates a car's value for tax purposes.