Police in Oklahoma are using scanners that can identify phony credit cards, but critics warn the devices could also allow cops to empty the bank accounts of law-abiding citizens with one swipe.

Authorities in the state are using the new devices during traffic stops to freeze and seize money loaded onto prepaid debit cards by alleged drug traffickers, with the potential to net up to $8,000 per portable scanner. Supporters of the program, which has only been in the field for about six weeks, say it's an important tool for law enforcement agencies to interrupt the flow of illegal drugs into Oklahoma.

Critics, however, are blasting the machines as a disturbing extension of civil forfeiture laws, with the potential for abuse by police and prosecutors. Opponents say such devices are an infringement on Fourth Amendment prohibitions of unreasonable search and seizure -- and that police departments are in turn stuffing their wallets with the cash from innocent civilians.

"We believe it’s blatantly unconstitutional," Nick Sibillia, of the Institute for Justice, told FoxNews.com. "The Fourth Amendment is unfortunately in tatters in this day and age."

The Oklahoma Department of Public Safety signed a contract with Texas-based ERAD Group Inc., to use the devices, which work on "open loop" prepaid debit cards, like those provided by American Express and Visa. But "debit cards attached to a valid checking account or valid credit cards cannot be processed" by ERAD, which stands for Electronic Recovery and Access to Data.

The company that manufactures the devices is also promised 7.7 percent of all money forfeited using the machines, according to one contract obtained by Oklahoma Watch.

"It's just absolutely appalling that a private company can profit from this forfeited property," said Sibillia.

The card readers, which are said to be used in at least 25 other states, have reignited debate over civil asset forfeiture -- a legal tool used by police and prosecutors across the country to take millions of dollars in cash, cars, homes and more every year.

Under civil forfeiture, law enforcement can seize property without charging an individual with a crime. Unlike criminal forfeiture, no conviction is necessary to seize assets -- a law opponents say threatens basic rights to property and due process.

Further, state and federal statute allows for cash and assets associated with the drug trade to become the property of a policing agency through civil litigation. In many places, cash and property seized boosts the budgets of the very police agencies and prosecutor’s offices that took it. In 2012, 70 percent of all forfeiture expenditures in Oklahoma funded salaries for law enforcement, according to data obtained by The Institute for Justice.

In the case of the ERAD system, the Oklahoma Highway Patrol says the machines are important in fighting identity theft and credit card fraud.

In an interview with FoxNews.com, Capt. Paul Timmons sought to clarify "misinformation" he said has made people panic.

"This is a tool for our troopers to use when they suspect there’s criminal activity," he said. "We don’t have access to anyone’s personal banking activity -- that’s all protected information."

On Monday, Oklahoma authorities also held a press conference to dispel rumors about the devices.

“We can do nothing with someone’s bank account. We can do nothing with someone’s debit card,” said Oklahoma Highway Patrol chief Col. Ricky Adams. “What we can tell is if it is yours, if the information on the back of a gift card is your personal credit card information.”

Oklahoma State Sen. Kyle Loveless, however, said he has major concerns over the system's use and the potential for abuse.

"The manufacturer in its patent and promotional videos said it can get information from any card with a magnetic strip," Loveless told FoxNews.com. "The issue is if it can take money from one card, it can take money from any card."

Loveless, a Republican, said many legitimate business use the cards targeted by ERAD machines. He also noted that prepaid cards are the only source of banking for many lower-income and young people and that unemployment, disability and other government assistance programs give money using prepaid cards.

Loveless called civil forfeiture a "growing problem" in the state, claiming most forfeitures there average $1200 and that Oklahoma counties are "taking in millions of dollars a year." He said one audit found that an Oklahoma district attorney used forfeited money to pay off his law school loans.

"The potential for abuse is basically a slap in the face of Oklahomans and Americans," he said.