GRANTS PASS, Ore. — Conservation groups are moving beyond the courtroom into the marketplace to pressure two of the nation's largest timber companies to green up their acts on private forest lands and challenge the timber industry's sustainable forestry standard.

In separate actions, Seattle Audubon Society and the Natural Resources Council of Maine are challenging green labels held by Weyerhaeuser and Plum Creek Timber Co., that certify their forests are managed in environmentally sustainable ways.

"Traditionally, environmental groups have used the courts to enforce the law," said David Ford, CEO of metaFore, a Portland-based nonprofit that helps companies assure the paper products they buy are produced sustainably. "Now that certification has come along and really is a voluntary market-based mechanism, it appears that they are looking to these standards and using the existing process."

Amid growing worries about global warming, major corporations — such as magazine publisher Time, Inc., and lumber retailer Home Depot — are demanding wood and paper products be certified as sustainable.

Ford said suppliers without a green label are sure to be hurt in the marketplace.

The complaints were filed this month with the Sustainable Forestry Board in Arlington, Va., which oversees the Sustainable Forestry Initiative, a green label developed by the timber industry, but now independent, covering 90 percent of the private industrial forests in the country.

The Seattle Audubon complaint alleges Weyerhaeuser has been logging too heavily in spotted owl habitat in southwest Washington.

The Natural Resources Council of Maine alleges Plum Creek Timber Co. should lose its certification after repeated violations of state logging standards, culminating in a fine of $57,000, the biggest in state history, plus logging in deer winter range and other problems.

Both complaints question the validity of the Sustainable Forestry Initiative standard.

Weyerhaeuser and Plum Creek denied violating their certifications.

The American Forest & Paper Association created the Sustainable Forestry Initiative in 1994 to encourage environmentally responsible practices, and it now covers 150 million acres in the U.S.

Environmental groups prefer the Forest Stewardship Council standard, based in Bonn, Germany, which was launched in 1993 after the Earth Summit in Rio de Janeiro failed to come up with one.

Shawn Cantrell, executive director of Seattle Audubon, said the timber industry standard "appears be an effort to greenwash," being "good on rhetoric" but flawed in practice, while the Forest Stewardship Council standard was better at getting good results on the ground.

Before filing the complaint, Seattle Audubon filed a federal lawsuit against the Washington Department of Natural Resources. It asks a judge to stop Weyerhaeuser from logging around owl nests on its land in southwestern Washington, claiming state logging regulations are not strong enough to protect the owl, a threatened species.

Weyerhaeuser spokesman Frank Mendizabal said they regularly leave more trees than required around owl nests, and characterized the sustainable forestry complaint as a tactic to win the lawsuit.

"We have not harmed any owls or done any work in habitat or reduced habitat for spotted owls or any other threatened or endangered species," he said. "Could (losing certification) affect our business? It might. It could. It's impossible to say."

Weyerhaeuser, based in Federal Way, Wash., owns 38 million acres of timberland around the world, with 6.5 million acres in the United States. Plum Creek, based in Seattle, owns 8.2 million acres of forest in 18 states, making it the nation's biggest landowner.

The Maine complaint is based on state documents detailing repeated Plum Creek violations of logging regulations from 1998 through 2002, and more recent logging in stands state biologists hoped to protect as winter shelter for deer. It also charges Plum Creek has been illegally clearcutting land it plans to develop as a resort.

"All those are repeated violations, not an, 'Oops, we goofed,' kind of thing," said Cathy Johnson, North Woods project director for the council. "Is that OK under the Sustainable Forestry Initiative? If it is, it certainly draws into question whether the Sustainable Forestry Initiative certification means anything at all."

Plum Creek spokeswoman Kathy Budinick said the company reported many of the violations of logging laws itself, has corrected them, and expects to be recertified next year.

"It is important to note that 99 percent of our lands we were managing properly," said Budinick.