Southwest Gas (SWX) started an underwritten secondary public offering of 9 million shares of Centuri Holdings (CTRI).

Underwriters are expected to get a 30-day option to purchase up to 1.35 million additional Centuri shares, Southwest Gas said Tuesday in a statement.

Southwest Gas also said it will sell $50 million of Centuri shares to Icahn Partners and Icahn Partners Master Fund, investment entities affiliated with Carl Icahn, in a concurrent private placement at the secondary offering price.

The private placement will likely close immediately after the closing of the secondary offering. Centuri is a former subsidiary of Southwest Gas.

Centuri shares slumped 9.4% in after-hours trading, and Southwest Gas fell 1.9%.