(Adds comments from union officials, Alcoa; background.)
By Nicole Mordant
May 15 (Reuters) - Negotiators for Alcoa Inc and unionized workers at 10 U.S. plants were "very far part" on several key issues, including wages and healthcare premium increases, with less than 12 hours before the expiration of their labor contract, the United Steelworkers said on Thursday.
Workers at plants including Alcoa's recently expanded Davenport Works facility in Iowa and fabricated aluminum products plant in Lafayette, Indiana have voted to give their negotiators the right to authorize a strike if a contract is not reached. The authorization does not mean the union will strike.
"The parties continue talking but as of late this morning they seem very far apart," said Wayne Ranick, the USW's director of communications, which represents some 6,100 Alcoa workers across the United States.
A previous four-year contract between the Pittsburgh-based aluminum producer and the union expires at 12:59 a.m. EDT (0459 GMT) on Friday.
If an agreement is not reached before the deadline, the two sides could extend the current contract talks if a deal looks close, workers could go on strike, or the company could lock out employees.
The last strike was in 1986 and lasted six weeks.
"The main sticking points are healthcare premium increases, wage package and two-tier benefits and pension packages for new hires," said Ken Cox, financial secretary of USW local 115, which represents workers at Alcoa's Lafayette plant.
The union has said it had "very modest" wage increases over the last two contracts.
Alcoa said its goal was to reach an agreement that was "fair to our employees and positions our business for future success."
"Alcoa and the USW have a proud history of working together, resolving problems and finding common ground, and we're confident that we will be successful in doing so again," company spokeswoman Monica Orbe said.
Negotiations, which began in Pittsburgh in April, come at a time when Alcoa has been cutting capacity at its smelters to stem a growing aluminum surplus that has depressed prices and made a large number of plants uncompetitive.
Alcoa shares fell 1.8 percent to $13.32 on the New York Stock Exchange amid a general sell-off of mining shares. (Reporting by Nicole Mordant in Vancouver and Cameron French in Toronto; Editing by Bernard Orr and Paul Simao)