BOSTON, May 25 -- The United Steelworkers union, which represents almost 6,000 workers at Alcoa Inc., said it's resisting the largest U.S. aluminum producer's efforts to "aggressively" cut benefits as a labor contract comes up for renewal.

Health-care proposals put forward by Alcoa may more than triple plan costs for some employees, Jim Robinson, the union's lead negotiator, said in an interview today. Costs for comprehensive family coverage would rise to about $315 a month, from $87 a month now, he said.

"That would be a huge increase in cost to the employees for inferior benefits," Robinson said. "The company is aggressively trying to reduce benefits and we're resisting. We'll see how negotiations turn out."

Alcoa and the union are working to avoid the first strike at the 11 plants covered by the contract in more than two decades. The union workers haven't had a strike since a 31-day outage in 1986, according to the union. The current contract expires May 31.

"Our proposal calls for a balance between excellent coverage and the costs associated with it," said Kevin Lowery, a spokesman for New York-based Alcoa.

The health plan being offered to the union is the same offered to 14,000 salaried and hourly employees in the U.S., Lowery said. The current union health plan costs Alcoa about 45 percent more per employee than the plan for salaried workers, according to the company's Web site.

Alcoa revised its proposal to bring down the cost of comprehensive family coverage to about $272 a month, Lowery said in a separate interview earlier today.

Alcoa shares fell 15 cents, or 1.4 percent, to $10.94 at 12:19 p.m. in New York Stock Exchange composite trading.