The National Transportation Safety Board (NTSB) is launching an investigation into Norfolk Southern’s safety practices as the company faces increasing scrutiny following a string of train derailments, including a high-profile derailment in Ohio last month, the agency announced Tuesday.

The NTSB said in a release it is launching a “special investigation” into the company, citing the “number and significance” of recent incidents involving Norfolk Southern. 

“The NTSB is concerned that several organizational factors may be involved in the accidents, including safety culture. The NTSB will conduct an in-depth investigation into the safety practices and culture of the company,” it said in a statement. “At the same time, the company should not wait to improve safety and the NTSB urges it to do so immediately.”    

Norfolk Southern has come under intense fire after a train carrying toxic chemicals derailed in East Palestine, Ohio, sparking environmental and public health concerns. A second train derailed in the state last week, but the cars were empty and no injuries were reported.

The NTSB said it has sent investigators to the sites of five “significant accidents” involving Norfolk Southern since 2021, including the death of an employee in an accident Tuesday.

The Norfolk Southern derailments have also placed federal rail regulations in sharp focus.

The federal investigation comes as lawmakers are pursuing legislation that would increase rail regulations and enhance safety measures. The bipartisan proposal, however, has run into Republican opposition in the Senate, because it leaves specifics up to the Transportation Department.