Aluminum producer Alcoa Inc on Monday posted its fifth net loss in the past six quarters, but when charges were excluded its results matched Wall Street estimates.

It benefitted from higher prices and said markets were improving, but Chief Executive Officer Klaus Kleinfeld also raised the possibility of strikes at its U.S. operations and revealed Alcoa recently lost a major beverage can customer.

In the U.S. we have about 5,350 employees that are covered under the USW (United Steelworkers union) master agreement. The master agreement expires on May 31 and we are currently in early negotiations, Kleinfeld said on a call with analysts.

Obviously we have a strong desire to reach a fair, as well as competitive labor agreement and to avoid any type of work stoppage. We've taken some steps to prepare in case the work stoppage would happen. He gave no further details.

Kleinfeld also disclosed the company was operating at a 75-percent utilization rate in manufacturing aluminum sheet, which is used for beverage cans.

We do see some destocking going on and we have lost one can sheet customer, he said, without identifying the company.

Asked about it, Kleinfeld said: We made the purposeful decision...once we had the chance to discontinue the large contract with one of our customers on the canned sheet side.

The 10-year contract had a lot of aspects in there that in total lost us quite a bit of painful as it is to make a decision like that and then having to curtail some capacity, he said.

In January, Chief Financial Officer Chuck McLane said Alcoa had eliminated its can sheet price ceilings to ensure the long-term profitability of the business and was passing on higher costs to customers.

In its earnings release, Alcoa said the its first quarter net loss was $201 million, or 20 cents per share, compared with a loss of $497 million, or 61 cents per share, in the same quarter of 2009.

The company reported a loss from continuing operations of 19 cents per share, while revenue rose to $4.89 billion from $4.15 billion, the Pittsburgh-based company said.

Excluding special items amounting to 29 cents, the company had a profit of 10 cents per share, which was the consensus of Wall Street analysts polled by Thomson Reuters I/B/E/S, even though they expected $5.238 billion in revenue.

Alcoa said restructuring and environmental costs, primarily from the decision to permanently close two smelters in Badin, N.C., and Frederick, Md., totaled $135 million, or 13 cents per share.

It also took charges for tax impacts totaling $112 million, or 11 cents per share, primarily as a result of changes in federal health care laws; and $48 million, or 5 cents per share for mark-to-market changes and the impact of power outages.

Alcoa said results improved over the 2009 fourth quarter, driven by price rises of 8 percent for aluminum and 13 percent for alumina, the metal's raw material.

But Doug Roberts, chief investment strategist at Channel Capital in Shrewsbury, N.J., noted revenue was short of what analysts were expecting.

Right now the company can make the numbers, but in essence what they're doing is cutting costs. It's still a cost-cutting story, not necessarily a revenue growth story.

Brian Hicks, co-manager of the natural resources fund of U.S. Global Investors in San Antonio, Texas, said: This seems like it's been an ongoing exercise for Alcoa, with restructuring and special one-time charges.

It makes the quarter a little bit messy. On a brighter note perhaps, they were able to contain costs this quarter.

Alcoa's stock closed up 18 cents, or 1.25 percent, at $14.57. It was down 8 cents in after-hours trading.

(Reporting by Steve James; editing by Andre Grenon and Carol Bishopric)