Story highlights $3,200 plane flight bill paid from Senate budget instead of campaign account

Landrieu's office says vendor billed wrong account, mistake has been fixed

Aide says media scrutiny of expense reports spurred a review of travel records

Sen. Mary Landrieu made headlines last November when she hitched a ride home on Air Force One with President Obama, but chose not to attend his event in New Orleans. Another lesser-known flight Landrieu took that same day mistakenly cost taxpayers more than $3,000.

CNN has learned that the vulnerable Louisiana Democrat used government money to charter a private plane to travel to a campaign fundraiser, in violation of federal law.

Landrieu spent more than $3,200 in taxpayer money to fly 400 miles round trip from New Orleans to Lake Charles, Louisiana, where she attended a $40-per person fundraising lunch with hundreds of women, according to Senate records and Landrieu campaign information. It is illegal to spend government money campaigning.

Landrieu's campaign spokesman, Fabien Levy, said in a statement that the charter company mistakenly billed Landrieu's Senate office instead of her re-election campaign. Levy said the campaign noticed the error a few weeks ago and asked the company to refund the Senate office and bill the campaign, which the company did. Levy said Landrieu's re-election campaign paid for the flight August 4, almost nine months after the November 8 trip.

"We take our finances very seriously and are glad we caught the vendor's mistake and were able to rectify the matter as soon as possible," Levy said.

The campaign didn't notice the mistake until July 29. Two days later, on July 31, USA Today published a story showing that Landrieu was one of the Senate's most frequent fliers, spending $47,000 last year on taxpayer-funded charter flights. Levy told CNN that media scrutiny of Senate office expense reports spurred the campaign to review its travel records.

Even though the mistake was corrected, the campaign still violated federal law and could face civil fines, said Paul S. Ryan, senior counsel at the Campaign Legal Center, a nonpartisan campaign watchdog.

"It is the senator and the senator's staff responsibility to comply with federal laws. It's not the job of the vendor, per se," Ryan said. "It sounds like their excuse is, 'We didn't do anything wrong; it's the vendor.' It's the job of the senator and her staff not to pay bills out of a Senate office account if those bills were not for Senate business."

Ryan argued that even though Landrieu fixed the error, the law should still be enforced.

"If senators were allowed to pay for their campaign expenses out of taxpayer dollars that challengers don't have access to, that's a major unfair advantage to incumbents," he said.

Landrieu took the charter flight the same day Obama delivered a speech on the economy in New Orleans. The senator cited her busy schedule as the reason she didn't accompany the President in her hometown.

"I was hosting a lunch in Lake Charles for 300 women and I wasn't going to stand them up. I'm sorry I couldn't be with the President," she told CNN's Wolf Blitzer a few days later.

At the time, Obama was under fire for the disastrous rollout of HealthCare.gov and breaking his promise that people could keep their health insurance coverage under Obamacare.

Landrieu's decision not to attend his event was widely seen as an acknowledgment that the President, who was already deeply unpopular in Louisiana, was a political liability for the vulnerable Democrat, especially since she cast a pivotal vote in support of Obamacare.