Issa's office said it received a phone call Thursday afternoon and an employee was told "that something had been left outside that would explode," the San Diego Union-Tribune reported. The staff immediately contacted the sheriff's office.
Vista bomb squad and fire personnel helped evacuate the building, Sheriff's Lt. Jim Nolan said..
Sheriff's Capt. Scott Rossall said the bomb squad and hazardous materials teams examined the bottle and concluded that it was not a threat. When asked if the bottle contained urine, Rossall said, "In looking at it, I'd say that would be a reasonable conclusion."
"Representative Issa in 2001 was the target of a bombing plot that was interrupted by the FBI," Frederick Hill, a spokesman for the Republican congressman, said in Washington.
"Particularly after the [Rep.] Gabrielle Giffords shooting, this is something that we, of course, take very seriously. Our first concern is the safety of Mr. Issa's employees working in Vista as well as the other occupants of the building."
Giffords is recovering from wounds suffered in a Jan. 8 attack by a gunman in Arizona that killed six people and wounded 13.
A small rally was held outside of Issa's office by MoveOn.org, an activist group, and members of Occupy North County about an hour before the threat was called in. Rossall said it was not known if the bottle was connected to the protest.
"I deeply appreciate the efforts of those from the San Diego County Sheriff's Office and the Vista Fire Department who responded to this incident," Issa said.