Precision Castparts and its welders are off to a difficult start, six weeks after nearly 100 workers voted to join a union.

Union organizers have filed four unfair labor action charges against PCC Structurals, a subsidiary of the Portland company. They allege that Precision Castparts has refused to recognize or bargain with the union, and that it's diverting work from its union welders to subcontractors.

Precision Castparts, meanwhile, continues to assert that the welders should never have been allowed to vote on unionizing.

The company maintains that its operations are "highly integrated" and so any union vote should have included a broader set of workers. PCC has appealed to federal officials to toss out the election's results and disputes the unfair labor practices allegation.

"Until the legal process is complete, PCC Structurals intends to await the outcome of the appeal before we commence bargaining," the company said in a written statement.

One of Oregon's largest companies, Precision Castparts makes large components for aircraft, electrical generators and other industrial products. Berkshire Hathaway, billionaire Warren Buffett's investment firm, paid $37 billion for the Portland company last year.

In its last year before the sale, Precision Castparts reported $10 billion in sales and $1.5 billion in profits.

Though more than a fifth of its 30,000 employees worldwide are covered by collective bargaining, Precision Castparts workers in Oregon have historically been non-union. In a 2013 vote of 2,300 workers in the Portland area, 57 percent voted against unionizing.

But this year's union drive tried a different strategy, seeking to get a foot in the door by organizing a smaller group of PCC employees. In September, welders voted 54 to 38 in favor of joining a union.

Billy Anderson, an organizer for the International Association of Machinists and Aerospace Workers, said he doesn't believe PCC will be able to replace its in-house welders with contractors. The PCC employees, he said, have years of experience that replacements cannot replicate.

Instead, Anderson said, he believes PCC is stalling while it assesses its legal options and trying to intimidate other employees who might organize. He said union members want to move forward with negotiations to achieve a level of dependability in work rules and pay.

"They voted for the IAM," Anderson said. "It's time to sit down and give those guys a fair contract."

-- Mike Rogoway; twitter: @rogoway; 503-294-7699