COLUMBIA -- The chairman of a congressional committee investigating the ongoing labor dispute over Boeing's North Charleston 787 assembly plant is prepared to use subpoenas to force labor officials to hand over documents from their investigation, according to a letter sent Tuesday to the National Labor Relations Board's chief attorney.

In the letter to NLRB general counsel Lafe Solomon, Republican U.S. Rep. Darrell Issa of California argues that Congress has the right to supersede attorney-client privilege in gathering information about the communications between the NLRB and Boeing, as well as the union that represents Boeing workers in Washington state.

The NLRB sued Boeing Co. in April, saying the aeronautics giant illegally retaliated against unionized Washington state workers when it opened a 787 passenger jet manufacturing line in South Carolina, a right-to-work state. Boeing already makes the planes in the Seattle area, and the company hopes more than 1,000 non-union workers will eventually build three of the aircraft per month at the

$750 million South Carolina plant, the largest industrial investment in the state's history.

Specifically, Issa asks Solomon to turn over his office's communications about the Boeing case, including any messages with NLRB officials other federal agencies or members of Congress. Issa says he also wants emails and call logs between the NLRB and Boeing, as well as NLRB's communications with the International Association of Machinists, the union that operates at Boeing's Washington state facilities.

"Attorney-client privilege is a judicially-developed policy intended to foster client confidence and encourage full disclosure to an attorney in anticipation of an adversarial setting," Issa wrote. "However, the need to protect this interest in an investigative setting where a congressional committee is not adjudicating the liberty or property interests of a witness is less compelling. ... Therefore, attorney-client privilege claims can be overcome by Congress."

Issa gives Solomon until July 26 to turn over the records or face a possible subpoena. An NLRB spokeswoman declined to comment on the request, and Solomon has said in previous communications to Issa that releasing some documents related to the case would compromise the case.

The labor case could drag on for years, and a Seattle judge has begun hearing arguments. Boeing has denied the charge, saying it opened the South Carolina plant for valid economic reasons. Last month, a federal judge handed NLRB an early victory, denying Boeing's request to toss the lawsuit.

In previous communications to Issa, Solomon has said he wouldn't turn over some documents, citing attorney-client privilege. Solomon initially resisted appearing when Issa brought his U.S. House Committee on Oversight and Government Reform to South Carolina for a field hearing last month, citing the ongoing legal case, but eventually relented and testified before the panel.

The lawsuit against Boeing has drawn outrage from Republicans who claim it interferes with the right of company managers to choose where and how to expand business operations. South Carolina Gov. Nikki Haley, a persistent union critic, has asked GOP presidential hopefuls stumping in the state -- home to the first-in-the-South Republican primary -- to weigh in on the dispute.

Haley has also called on President Barack Obama to tell the NLRB to back off. Obama, who has declined to criticize or openly support the actions of the NLRB, an independent federal agency, last week called on Boeing and its workers to resolve their differences, saying that businesses should generally be able to locate where they want but must follow the law.

Delivery update

Boeing Co. said Tuesday that a temporary halt on the delivery of 787 parts has no impact on employment at its North Charleston campus.

"We're still busy," said spokeswoman Candy Eslinger.

Boeing has suspended deliveries of 787 airplane sections from its suppliers, including its North Charleston operation, to the assembly line in Everett, Wash., and will hold the line in place for a month while mechanics catch up on work.

The local site, which now has several thousand workers in three plants, has experienced similar slowdowns before, Eslinger said.

"It is not any different than the other ones we've been through," she said.

One of company's plants at Charleston International Airport makes aft fuselage sections for the 787. A nearby factory modifies mid-fuselage sections made in Italy.

Boeing workers in North Charleston are now gearing up to assemble up to three 787 jets a month at a third plant. Production is expected to begin this month. The first 787 delivery from the South Carolina plant is set for early next year.

"It's a gradual ramp-up ... and it's all on schedule," Eslinger said.