Securities regulators have opened an inquiry into the way Goldman Sachs, Citigroup and other banks divvy up new bond issues among investors, people familiar with the matter said.

The Securities and Exchange Commission has sent requests for information about how banks allocate corporate-bond deals and how they traded those bonds after they were sold, the people said. The regulator is examining whether banks grant some money managers too much influence in these offerings, leaving smaller bond investors at a disadvantage, said the people.