The union represents factory workers who assemble some of the company’s best-selling planes.

The strike is stretching on as Boeing deals with multiple other issues. It has shut down production of 737s, 777s and 767s. Work on 787s continues with nonunion workers in South Carolina.

S&P Global Ratings put Boeing Co. on its “CreditWatch Negative” list this week, citing increased financial risk because of the strike.

The addition to S&P’s CreditWatch means there is an increased likelihood of a credit downgrade, which could make it more expensive for the company to borrow money.

Shares of Boeing, which is headquartered in Arlington, Virginia, fell almost 3% at the opening bell Wednesday and the stock is down 41% this year.