Sen. Dianne Feinstein said, “It is hard to believe that there is not already a federal (statute) to punish those involved with the financing, construction and use of these tunnels.”

But Feinstein, D-Calif., is one of the main advocates of a tunnel-criminalization effort that is reaching fruition with the inclusion of the measure in legislation to fund the Department of Homeland Security.

The Border Tunnel Prevention Act would impose criminal penalties of up to 20 years in prison for those who construct or finance tunnels, which have proliferated in recent years in San Diego County and other border areas. It would permit a 10-year sentence for people who allow their property – including the buildings where the tunnels meet the surface – to be used by the tunnel builders.

The bill would solve a fundamental problem for federal law enforcement authorities. Under current law, they can only prosecute tunnel builders who are implicated in the smuggling of contraband or illegal immigrants through the underground passage.

Rep. David Dreier, R-San Dimas, who carried the bill in the House of Representatives, called it “a common sense reform.”

“We have a problem that needs to be addressed, and it's being addressed in a bipartisan way,” he said during debate on the measure.

Over the past five years, according to Feinstein's office, at least 44 border tunnels have been discovered, all but one between the United States and Mexico.

While officials suspect the tunnels are primarily used to smuggle drugs, they have raised other concerns about them.

“A tunnel can be used to smuggle drugs, illegal aliens, weapons and possibly weapons of mass destruction into the United States,” said special agent Steve Robertson of the Drug Enforcement Administration.

Paul Charlton, U.S. attorney for Arizona, said that Justice Department policy bars him from commenting directly on pending legislation. But, he said, “As we are more successful apprehending those who come (illegally) above ground, there will likely be more people interested in coming across below ground.”

Last March, Charlton's office won a conviction against Mexican architect Felipe de Jesus Corona-Verbera, who masterminded the construction of a tunnel between a house in the Mexican border town of Agua Prieta to a warehouse in Douglas, Ariz.

But Verbera was convicted on smuggling charges for his involvement in the movement of 2 tons of cocaine that were brought through the tunnel and shipped to Phoenix, where authorities seized the contraband.

The new legislation is one of the least controversial border measures ever brought before Congress. It sailed through the House of Representatives last week, 422-0. It was then added to a House-Senate conference report for Homeland Security funding, which is expected to sail through both houses on a final vote.

Efforts by Republican lawmakers to pass more comprehensive immigration legislation foundered on intraparty disagreements over whether to get tougher on illegal immigration or create a pathway to citizenship for millions of undocumented immigrants. The border tunnel bill may be one of the only measures to survive the debate before Congress breaks for a pre-election recess.