Ford (F) has been put under the microscope by two U.S. senators that are calling for an immediate investigation of the company’s Focus and Fiesta vehicles. Ford allegedly knowingly sold the cars with a defective transmission, following thousands of complaints and a number of repairs, the Detroit Free Press reported.

The issue with vehicles’ transmissions stems from an alleged slipping of the dual-clutch DPS6 transmission into neutral, which can cause the cars to lose acceleration at times or jump forward unexpectedly. The issue has caused a series of accidents and as many as 50 injuries, according to customer complaints, the news outlet said.

U.S. Sen. Richard Blumenthal and U.S. Sen. Ed Markey told the news outlet in a joint statement that “Ford knowingly put American families and children at risk – this indifference to safety is inexcusable.

“NHTSA must take the thousands of complaints it has received from scared consumers seriously and immediately open a defect investigation into the Ford Fiesta and Focus vehicles to identify how deep Ford’s lies are buried," they added.

Both Markey and Blumenthal serve on the Senate Committee on Commerce, Science, and Transportation.

Ford responded to the call for an investigation, with spokesman TR Reid telling the news outlet, “Automobiles using the DPS6 transmission were and remain safe to drive. Ford’s work and comments on these vehicles have always been thorough and truthful.”

The transmission issue was brought to light in 2014 when the National Highway Traffic Administration (NHTSA) decided not to open a formal investigation after the automaker added an “overt-warning” light indicator in 2015 to notify drivers that the transmission was malfunctioning.

Reportedly there have been as many as 4,300 complaints related to the transmission issues in the 2011 to 2016 Fiesta and 2012 to 2016 Focus cars.

The NHTSA told the Detroit Free Press in a statement that, it “shares the sense of urgency about this and other high-priority safety concerns. Our mission as an agency and the approach that we take to our review of every safety matter is founded on concern for public safety and a reliance on data, science and facts.

“NHTSA continuously monitors a variety of data sources, including media reports and consumer complaints, revisits issues as appropriate, and will not hesitate to take action if and as warranted to ensure safety. NHTSA will, as always, act appropriately and responsibly related to any safety matter when there is evidence of an unreasonable risk to safety.”

As many as 1.5 million Ford Fiesta and Focus vehicles equipped with a DPS6 transmission are in drivers’ possessions, which the news outlet reported that as many as 350,000 of the vehicles have been repaired three or more times.

Ford has not issued a recall for the alleged transmission issues in the Focus or Fiesta vehicles to date.

Ford Focus NY Dealership 2013 Getty 2
A Ford Focus sits on display at a Manhattan car dealership that sells Ford vehicles in New York City. Getty Images