It had been 30 months since Elaine Brown, the mother of two teenage daughters, received a child-support check from her ex-husband. So when she discovered a private company that could locate delinquent parents, she eagerly signed up.

She could accept that the firm she hired in June -- Supportkids Inc., based in Austin -- would take a 34 percent commission out of the $4,000 she was due. Only later did the mother realize what the consequences of that arrangement would be.

Because delinquent parents rarely pay the money they already owe -- it's hard enough to get them to start making their regular support payments -- the company takes its cut from all future checks received, in theory until the debt is paid. But that day often never arrives.

Critics also say the company takes its share of the support checks even if it was not directly responsible for the money showing up, such as when the government garnishees a delinquent parent's wages.

"This just isn't right," said Brown, 37, an office manager for a health care firm in Oak Park, Ill. "At the time I signed on with the company, I was anxious and desperate, but I paid a steep price."

At first glance, private, for-profit agencies seem like a smart way to cut through the snarled child-support collection system and reduce the $89 billion backlog owed by noncustodial parents in the United States.

But rather than find relief, some parents say they've been victimized again -- and are fighting back.

Charles H. Barr, a Milwaukee attorney who recently filed suit against Supportkids, alleges that the firm -- the nation's largest -- uses "false and misleading representation" to woo parents.

Barr sued on behalf of a Whitelaw, Wis., woman but hopes to certify a class of plaintiffs nationwide who find themselves in similar straits. A Wisconsin judge is expected to make a ruling on the class-action request later this fall.

"The ads promise that the company only gets paid if they collect, which is simply not true," Barr said.

Clients also cannot cancel the contract if they are unhappy with the firm's work, he added. "It's unconscionable . . . in that it takes advantage of the most vulnerable parents and children."

It's not the first time these franchises have been in legal hot water. In 1999, the Illinois attorney general's office sued two companies -- one in Rockford, Ill., the other in Houston -- that allegedly were swindling single parents. The Rockford firm is out of business; the other, Child Support Assistance Network, is negotiating a settlement with the state.

But supporters of this type of company say the private sector fills a critical need for parents with few options.

"The government fails to collect on six out of 10 cases," said Kathleen Kerr, chief operating officer for Supportkids, noting that the typical client has not received support in four years and is owed an average of $25,000. "Where are those people supposed to go? They have the right to pay to get help."

The dispute sheds some light on a little-known industry that scarcely existed a decade ago. Since 1990, about 38 firms -- with names such as Kids Ltd. and Support the Children -- have sprung up.

The firms employ highly trained investigators with a small caseload, allowing them to commit more time and resources to individual cases than the government can, according to the Child Support Enforcement Council, a national association of private collection agencies.

"We're aggressive," a spokeswoman said. "And we don't take no for an answer."

Once the parent is located and persuaded to pay up, checks are rerouted to the company, which takes out its fee before giving the client the rest. The companies typically market themselves via the Internet or by advertising on cable networks that target a female audience.

Although the 1996 welfare reform act mandated that states crack down on deadbeats, chasing delinquent parents continues to be a difficult task.

Stepping into this void are the modern-day bounty hunters.

"We work the toughest cases . . . the ones the states have given up on," said Kerr, whose company, she says, has retrieved more than $120 million in the last 11 years.

Kathleen Nilles says Supportkids helped her collect on 18 years of past support from her ex-husband, even though the child-support enforcement office in Rockford, Ill., told her that the statute of limitations had run out.

"This is money I never thought I'd see," Nilles said. "They did everything they said -- and more."

But Brown's experiences were less satisfying. When her ex-husband fell behind in his payments two years ago after a job change, she saw a Supportkids commercial, signed a contract and mailed in her court orders. She also authorized a change-of-address form that rerouted any support checks to the Austin office.

"But I never could get a breakdown of expenses in writing -- exactly how much they would get and for how long," she said.

Now, because of the company's commission, she's getting $117 every two weeks rather than $147, which has squeezed her budget at precisely the time her two daughters, 14 and 18, are thinking about college.

Brown said she would have been better off forgetting the arrearage in exchange for payment of current support, not subject to the fees. "I took a shortcut and made a big mistake," she said.

Patricia Zipperer, 35, the plaintiff in the lawsuit, expressed similar regrets. She hired the company in July 2001 to retrieve $9,500 owed by the father of her 14-year-old son.

Soon, instead of $270 a month, she was getting $183.48 -- but the real shock came when she discovered that Supportkids apparently did little or nothing to earn the commission. The company took its fee out of wage garnishments made by the Oconto County, Wis., child-support office.

"When I heard that, my heart just stopped," said Zipperer, who works two jobs and has two preschoolers

In November, she repeatedly wrote letters and sent e-mail messages to try to terminate the firm's services. After repeated demands and intervention from the Wisconsin Consumer Protection Office, the company closed her case last March, according to the suit.

"They said they had all these investigators diligently working on my case -- but nobody ever called me," Zipperer said. "They were only interested in me when they were getting me to sign up. After that, I never talked to anyone."

According to Kerr, "It is not Supportkids' policy to take fees on support we did not collect. We regularly pass through payments, such as IRS intercepts, to our clients without taking a fee."

Still, she added: "All monies come in from state disbursement offices, and all of the checks look identical. . . . This is a critical area where greater cooperation between public and private agencies would best serve the families."

The fees and contracts are essential for private companies to be able to offer their services to people who could never afford fees for attorneys and investigators, according to the Child Support Enforcement Council. "Someone has to pay for this."