Giffords was taking part in the signing ceremony at the White House. She resigned from Congress last month as she continues to recover from a gunshot wound to the head.
The legislation increases the penalties for using ultra-light aircraft when smuggling drugs into the country. The small, single-seat planes are an increasingly favored tool that smugglers use to fly at night and then release their haul without detection.
Giffords stepped down on the day the House passed her bill by a vote of 428-0. She has focused on her recovery and said she will eventually return to public service.