Issa has said that the NLRB's case against Boeing appears to be politically motivated, but Democrats said in their letter that it was Issa who was taking sides in the matter.
“One serious concern with compelling the production of these documents at this time is that you appear to be using the authority of the Committee in an inappropriate manner to assist a private party, Boeing, during ongoing litigation,” the letter said.
Before NLRB general counsel Lafe Solomon testified at an Oversight Committee field hearing in South Carolina, Issa had agreed to limit the scope of his inquiry into documents that would be "discoverable" in the ongoing case.
Boeing opened its new plant last month in Charleston, S.C. If the NLRB complaint is ultimately successful, however, the company could be forced to build the planes it intends to build there in Seattle instead.
An administrative law judge in Seattle dismissed a Boeing motion to dismiss the case at the end of June. The case is expected to last several weeks.