WASHINGTON -- Florida Sen. Bill Nelson is one of two U.S. senators calling on federal officials to investigate the vendor that manages SunPass tolls amid ongoing problems with the system.

In a letter sent Monday to Federal Trade Commission Chairman FTC Chairman Joseph Simons, Nelson and Sen. Gary Peters (D-Mich.) are asking the agency to take action against Conduent. They say the company has violated the FTC Act, which bars unfair and deceptive trade practices.

The SunPass toll collection system hasn't been fully operational since a botched multimillion-dollar platform upgrade last month. Tens of millions of toll transactions have been backlogged, causing headaches for motorists who rely on toll roads for work. 

The Florida Department of Transportation has suspended late fees and penalties until the system can be fixed, and it's demanded that Conduent provide an end date to the repair work.

In addition to Florida, Conduent has faced scrutiny of its toll system operations in Michigan, California, Texas, New York, New Hampshire and Maryland.

"Conduent's pattern of mismanaging cashless toll systems is deeply troubling and warrants further scrutiny," the senators wrote. "If drivers are being hurt financially, the FTC should hold the company accountable and prevent it from doing further harm."

Nelson is in Orlando and the Tampa area today, and we'll be asking him about SunPass. Check back for updates on this developing story.