Two Dominion subsidiaries began locking out 915 union-represented employees across six states Wednesday until negotiations on a new labor contract are completed.

The previous labor contract expired in April, with the union members agreeing to continue working during negotiations. Dominion’s decision to lock out the union members would avoid the threat of a strike during the heating season.

The employees impacted by the lockout belong to the United Gas Workers Union Local 69, including 150 workers for Dominion Hope and more than 760 employees of Dominion Transmission Inc. (DTI). The lockout affects workers in Maryland, New York, Ohio, Pennsylvania, Virginia and West Virginia.

“Our top priority is to safely and reliably meet the energy needs of our customers,” Dominion Hope VP Jeff Murphy and Dominion Hope and DTI VP Brian Sheppard said in a joint statement. “Given the actions of the union leadership, we feel we have no other choice with the heating season approaching.

“The uncertainty of the labor situation could leave our customers literally out in the cold. We cannot let that happen, so our companies have had to make a very difficult decision. We are taking the steps necessary to ensure continued safe operations and reliable service.”

The two sides have failed to find common ground on Dominion’s proposal to eliminate retiree medical benefits for new employees. In a letter to its members, the union’s board said “it could not agree to that because it would create a two-tier system within our bargaining group. The union has made and will be making proposals to the company that will save it more money than the very proposals that the Company wants” the union to accept.

The union said it never threatened to strike and would have agreed not to strike if Dominion had agreed not to lock out its members.

“There was no need for this lockout,” the board said.

Dominion said it is committed to avoiding service interruptions during the lockout and will be bringing in contractors and temporary workers to assist its nonunion personnel.