Hidden cameras and microphones placed by federal agents in a house in Lynden, Wash., paid off recently when officials uncovered a plot to dig a drug tunnel from Canada to the United States.

But because federal officials used a provision in the U.S. Patriot Act (search) to bug their suspects for weeks, some groups are calling the search warrants an abuse of power.

"We want them to be able to accomplish their objective. We don't want law enforcement officials to be able to run roughshod, investigating for whatever they want with whatever rules they set," said David Keene, chairman of the American Conservative Union.

Click in the video box to the right for a complete report by FOX News' Dan Springer.

Delayed notification, or so-called "sneak-and-peek" (search) warrants, have been around since 1973 and require prosecutors to go to a federal judge to get permission to search. But until the Patriot Act, federal officials needed to show probable cause and tell the suspects they're under surveillance within seven days.

Now, the evidence bar is lower and the surveillance can go on indefinitely so long as a judge is convinced it is needed — all without the suspect's knowledge.

"From a law enforcement standpoint, there's no question we're protecting civil liberties, they're rarely granted, they're supervised by federal judges and in this case, it was highly effective and highly necessary," said John McKay, the U.S. attorney in Seattle who sought warrants in the drug tunnel case.

"We do not want to give up on freedoms guaranteed by the Constitution, but at the same time, we have to say 'We've got to protect this country,'" added U.S. Rep. Dave Reichert (search), R-Wash.

But critics point out that the Patriot Act was supposed to be a tool in the War on Terror (search), not the drug war, even though the original sneak-and-peek rules were aimed at organized crime and drug traffickers.

"What we've learned from history is that if we grant powers that can be abused, they will eventually be abused or misused or used in other ways," Keene said.

The Patriot Act is up for renewal in Congress. The House voted to keep the law just as it is now but the Senate version placed limits on the sneak-and-peek warrants. The two chambers now have to hammer out a compromise.