Two unions representing hourly workers at DuPont and Chemours have called on the US chemical giant and its recent spin-off to cooperate with workers on safety issues in the wake of scathing allegations from federal regulators.

In a letter to company executives, the presidents of the United Steelworkers (USW) union and the International Chemical Workers Union Council (ICW) wrote that they would prefer to improve safety measures through collaboration rather than complaints from the US Occupational Safety and Health Administration (OSHA) and the National Labor Relations Board.

USW president Leo Gerard and ICW president Frank Cyphers noted that DuPont previously enjoyed a "good relationship" with its unions on safety issues but inspections by union-hired safety experts slowed in recent years, and the results was a series of citations.

The latest, issued in July, placed DuPont in OSHA’s Severe Violator Enforcement Program over an accident that killed four workers at a La Porte, Texas plant.

OSHA regulators said that "the very serious hazards we uncovered at this facility are evidence of a failed safety program."

Urging company executives to “reach out and begin collaboratively addressing safety concerns,” the union official said, “we are confident that a close and mutually respectful relationship can improve safety far more effectively."

Both DuPont and Chemours reportedly have pledged to involve unions in the future in addressing local safety concerns at local plants.