General Electric Co. said securities regulators have opened a probe into the company’s accounting practices, a new challenge to the conglomerate’s efforts to untangle its problems and turn around its struggling business.

The Securities and Exchange Commission is investigating how the company recognized revenue from long-term service contracts for projects like power-plant repairs and jet-engine maintenance, GE said. The Boston-based giant, which reported revenue of $122 billion for 2017, has about $15 billion of such service...