Horizon Lines Inc., which operates Hawaii's second-largest ocean shipping line, plans to cut its nonunion work force by at least 10 percent, or about 70 of its 700-plus nonunion employees, to save an estimated $7 million to $10 million in annualized labor-related costs.

The Charlotte, N.C.-based company said yesterday it will offer a voluntary severance program to eligible nonunion employees. But Horizon added that if it is unable to achieve anticipated reductions from the program, it will implement an “;involuntary”; severance program for nonunion employees.

Jim Storey, director of investor relations and corporate communications for Horizon, said it's too early to know whether the Hawaii work force will be affected.

“;This is a process where we're asking for volunteers and it's not targeted at any one geographic or operational area,”; Storey said. “;It's hard to say what impact it would have on any one specific area. It all depends on who steps up and volunteers and whether the person who volunteers is accepted.”;

Horizon said it expects to complete the work-force reduction by Jan. 31, 2009, and it is expected to result in a fourth-quarter pretax charge of about $3.5 million to $5 million, or 11 cents to 16 cents a share.

“;We continue to face a very difficult macro-economic environment that is having a significant adverse impact on the markets we serve,”; said Chuck Raymond, chairman, president and chief executive of Horizon.

Horizon, which accounts for about 37 percent of the total U.S. marine container shipments from the mainland to Hawaii, Alaska, Puerto Rico, Guam and Micronesia, operates four ships on mainland-Hawaii-Guam routes and an additional five that travel between the mainland and Asia.