FONTANA, Calif. (AP) — Investigators wearing bulletproof vests sit in unmarked cars outside a Southern California recycling center, swapping license plate details over two-way radio before dawn.

A truck emerges and they follow, hoping to learn where drivers pick up what to many looks like trash but turns out to be treasure: cardboard.

"It's big, big money — for somebody," said Steve Rivera, a senior investigator with the San Bernardino County District Attorney's office who has been conducting sunrise surveillance to track, educate and cite the culprits. "People don't recognize the fact that it's actually theft."

The crackdown in gritty, industrial suburbs east of Los Angeles aims to put a stop to a long-running practice that surges with cardboard prices and wallops trash company revenues — and could eventually push up trash collection rates for homeowners and shopkeepers.

New York City has battled cardboard theft for years. Local authorities elsewhere have cited those who swipe recyclables from waste hauler-provided bins, but the efforts haven't curtailed the theft of cardboard, which can net anywhere from $100 to $200 a ton.

When the economy booms, cardboard prices rise as manufacturers make more goods and need more packaging to sell them. Thieves are more brazen, and steal much more, when cardboard prices peak.

Waste haulers count on selling the recyclables they retrieve at the curb to offset the cost of collection, industry experts said.

"Our industry loses millions of dollars a year due to cardboard," said David Biderman, general counsel for the National Waste & Recycling Association. "One piece of cardboard by itself isn't valuable. But customers often generate substantial values of it."

The price of cardboard currently hovers around $100 a ton — much higher than during the 2008 recession but down from last year due to weaker demand from China, which is the largest export market for U.S. cardboard, Biderman said.

Under most state and local laws, people can collect cardboard left outside by a business or doled out by a shopkeeper for recycling. But they can't remove materials from recycling bins left out at the curb, which are considered property of the local waste hauling company, said Ronald Steiner, a professor at Chapman University law school in Orange County, who teaches case law related to privacy rights and garbage.

In San Bernardino County, officials are citing offenders with misdemeanor petty theft. So far, two citations have been issued, Rivera said.

In Huntington Beach, California, about half to three-quarters of the cardboard placed in commercial bins is stolen before drivers can retrieve it, said Sue Gordon, vice president of public affairs at Rainbow Environmental Services.

"They know our routes and they get there before we do, and they pop the lock and they pull it out," Gordon said.

In San Bernardino County, at least one hauler is considering raising rates to offset the lost revenue.

Burrtec Waste Industries, which is working with county investigators, has seen the problem grow since a California law required many businesses to recycle, which has meant more trips for trash trucks but also more thieves, said Michael Arreguin, the company's vice president.

"We can't absorb it completely as a company," Arreguin said. "If it continues, the return value of the material has to go down, and therefore it increases the cost of that recycling container."

Cardboard theft also makes it harder to determine whether the state is meeting mandated recycling goals, he said.

Neighbors often complain about residential scavenging, fearing those rummaging through their trash bins might find information that could make them susceptible to identity theft. Others are more sympathetic to homeless scavengers seeking bottles and cans to make a meager living.

Authorities say cardboard theft occurs on a much larger scale in commercial areas where big box retailers unload tons of the material along with their merchandise, but law enforcement rarely has time to police it.

Cardboard thieves drive pick-up trucks fitted with rails to prevent the material from flying away, or trailers, so they can pack more in. Some drivers douse the material with water to make it heavier, and fetch more money at recycling centers, said Rivera, who has conducted surveillance on more than a dozen trucks, some of them trekking miles to retrieve cardboard, since last year.

In Fontana, California, authorities from the district attorney's office recently pulled over one driver whose pickup was brimming with a tower of flattened boxes. They were concerned about the stability of the load, and wanted to determine whether the cardboard was legally obtained.

In that case, 47-year-old Ramon Sucilla had been legitimately given the material by a local furniture store owner on the premise they'd split the recycling proceeds.

Sucilla said he'd rather be holding down a warehouse job, but when work is scarce, cardboard helps make up the difference.

"I don't know how thieves would steal it, or when, because it takes time," Sucilla said, adding it took him nearly two hours to load half a ton of cardboard worth $50. "People who do this, at least those who do so honorably, they do it out of necessity."