Singapore Post said on Sunday it had dismissed its chief executive and two other senior managers after an internal investigation found they had mishandled whistleblower allegations about misconduct by company employees.

Singapore Post Ltd. shares slumped by the most in more than four years after the firm fired its chief executive officer and a number of other senior executives following allegations related to its international e-commerce logistics parcels business.

Singapore Post has fired its group chief executive and two other senior leaders after finding them negligent in the handling of a whistleblower report related to the company’s international business operations.

Singapore Post on Sunday said it had dismissed its chief executive and other senior managers following an investigation into allegations around its international e-commerce parcels business. The firm,

In a statement released on Sunday, the Temasek Holdings-backed company revealed that investigations were launched after receiving a whistleblower report.