Frustrated after more than nine months of contract negotiations with the West Coast dockworkers’ union, the chief executive of the shippers bargaining group Pacific Maritime Association on Wednesday revealed details of its offer to the union in a conference call and threatened a shutdown of operations at West Coast ports.

“We have a responsibility to let people know of the critical place we’re at now,” said James McKenna, the association’s chief executive.

The conference call was the association’s most public step yet in its long-running negotiations with the International Longshore and Warehouse Union, which started in May. Asked why the Pacific Maritime Association was now publicizing details of its negotiations, McKenna said, “We’re trying to get the ILWU to accept our contract proposal.”

If the union doesn’t accept, McKenna said he anticipates shipping companies and terminal operators will shut down operations and lock workers out of West Coast ports sometime in the next five to 10 business days.

The current five-year contract proposal offered by the association is final, McKenna said. The proposal includes a 3-percent salary increase, the continuation of a generous health insurance package, a pension bump and an agreement that repairs to truck chassis – trailers used to haul cargo containers in and out of the ports – will be made by ILWU members.

“The PMA has concluded the latest offer is the farthest we can go to this point,” McKenna said.

Union representatives did not return a request for comment.