A month-long lockout at the fourth-largest aluminum smelter in the United States ended on Thursday after unionized workers voted to ratify a new five-year labor deal with Century Aluminum, the union said on its website.

The United Steelworkers Local 9423 and Century, controlled by Swiss commodities trade house Glencore, resumed negotiations last week over a labor deal at the 244,000 tonne-per-year Hawesville, Kentucky, smelter.

Workers approved the deal by a 68 percent 'yes' vote.

The vote came after the more-than 560 union members rejected four previous tentative agreements on a new deal after the prior one expired on March 31.

Century repeatedly said output would not be affected by the lockout and hired temporary, non-union workers to operate the facility during the dispute.

Cable and wire manufacturer Southwire, which is Century's largest customer and operates an aluminum rod, wire and cable plant next door, has said it took steps to ensure it maintained an adequate supply of aluminum and that it saw no disruption as a result of the lockout.

The new tentative agreement lowers future healthcare premiums and contains modified language regarding employee overtime, Century sai.