The United Steelworkers union has asked more than 14,000 of its members at facilities run by ArcelorMittal, the world’s largest steelmaker, to allow it to call a strike if ongoing contract negotiations fail.

The Pittsburgh-based labor union said in a notice distributed at 14 plants nationwide that a “lack of progress” in the talks, which began four months ago, prompted the strike authorization vote scheduled for today.

The union has been negotiating with Luxembourg-based ArcelorMittal SA on behalf of the workers and tens of thousands of retirees. The current contract expires Sept. 1.

ArcelorMittal says it remains optimistic an agreement will be reached.

The United Steelworkers cited a tentative four-year deal it reached earlier this month with United States Steel Corp. covering some 16,000 workers at domestic flat-rolled and iron ore mining plants, as well as tubular operations in Ohio and Alabama.

ArcelorMittal’s “current position does not do justice to our needs and demands and does not match the pattern set by the U.S. Steel agreement,” the union said in the handbill to members.

Among the contentious issues are premiums for retiree health care, company contributions to a trust fund for health care, employee incentives, a profit-sharing agreement and capital investments, according to the union.

Tony Montana, a union representative participating in the negotiations, said a work stoppage is still avoidable.

“But we need to prepare our members for the eventuality that they could be called on to start manning picket lines,” he said.

Bill Steers, an ArcelorMittal spokesman, said the company believes both sides “continue to be committed to the process.”

“We are optimistic that a fair and reasonable settlement will be reached before the contract expiration date,” he said in an e-mail message.

ArcelorMittal has more than 320,000 employees in more than 60 countries, including about 18,000 employees at 17 facilities in the United States.

The company turns out a tenth of the world’s steel. It has said it plans to increase shipments by more than a fifth by 2012 as it pushes into Latin America, Africa, Eastern Europe, Russia and Central Asia, pointing to strong worldwide demand.