Gabrielle Giffords' final piece of legislation is now law.

President Barack Obama signed the bill in the Oval Office at the White House on Friday with the former Arizona congresswoman and her husband, Mark Kelly, looking on.

The the Ultralight Aircraft Smuggling Prevention Act of 2012 closes a loophole that treated the use of ultralight aircraft to help with drug smuggling different from the use of other aircraft. Now, their use can bring a long jail sentence and stiff fines.

Ultralights weigh less than 254 pounds and have a single seat, according to FAA classifications.

For years, Customs and Border Protection officers have tracked small aircraft crossing the U.S.-Mexico border to bring drugs into the United States.

Between 2009 and 2011, more than 600 suspected ultralight aircraft were detected crossing the border, and nearly 400 were confirmed, according to CBP data.

"It's an increasing problem," said a CBP official in Arizona not authorized to speak publicly. "This didn't use to be a problem at all," he added, but because other ways to stop drug traffickers at the border have been successful, "they have started to resort to this type of activity."

Ultralights typically can carry as much as 250 pounds of drugs at one time, he said. Sometimes, traffickers drop the drugs and fly back to Mexico, while other times, they land, unload the drugs and refuel.

The new law treats ultralight aircraft used in smuggling operations the same as larger planes. Penalties can now reach up to 20 years in jail and $250,000 in fines.

At the bill signing, Obama praised Giffords' work. "She has spent her career fighting for the safety of the people of Arizona, and the fact that it passed unanimously shows just how much Gabby is respected by her colleagues in Congress in both parties." he said. "I'm confident that while this legislation may have been her last act as a congresswoman, it will not be her last act of public service."

Giffords was shot in the head on January 8, 2011, while at a constituent meeting in her home district in Tucson, Arizona. She left Congress last month after voting for the ultralight bill. She said she wants to focus on her recovery but vowed to come back, saying in a statement, "I will return, and we will work together for Arizona and this great country."