A military cargo plane carrying three US senators and a member of the House of Representatives came under fire shortly after taking off at Baghdad.
Sen Martinez said that he saw a bright flash outside the window
The lawmakers said their plane, a C-130 Hercules, had to avoid three rocket-propelled grenades over the course of several minutes.
After taking evasive action, they safely completed their journey to Amman in Jordan.
"It was a scary moment," said Republican Senator Mel Martinez.
"Our pilots were terrific," he said. "They banked in one direction and then banked the other direction, and they set off the flares."
Flares can distract rockets that have heat-seeking guidance systems.
Two other Republican senators, Richard Shelby and James Inhofe, and Democratic Representative Bud Cramer were also on the plane.
C-130s are often used to ferry dignitaries around trouble-spots
"We were jostled around pretty good," said Mr Cramer, who estimated the plane had ascended to about 6,000 feet (1,830 metres).
"There were a few minutes there where I wondered, 'have we been hit? Are we OK?'"
Sen Shelby added: "I was looking out the window, a little small window, and I saw a shell or something.
"And then I see a flare. Our plane started manoeuvring and changing directions and shaking all around."
Lawmakers travel to Iraq regularly to take a closer look at the military and political situation, usually staying inside Baghdad's secured Green Zone and travelling under heavy security.
Sen Shelby, Sen Martinez and Mr Cramer said the recent increase in US troop levels had helped stabilise parts of the country.
"It was kind of dicey," Sen Shelby told Associated Press of the incident. "But it just shows you what our troops go through every day."