Boeing will lay off more than 2,500 workers in the U.S. states of Washington, Oregon, South Carolina and Missouri, according to federally required filings posted on Monday and a union official, as part of the debt-heavy U.S. planemaker's plan to cut 17,000 jobs, or 10% of its global workforce.

Nearly 2,200 layoff notices went to workers in Washington and another 220 in South Carolina, the two states where Boeing builds commercial airliners. Boeing declined to comment on the layoffs on Monday.

The aerospace giant started telling affected U.S. workers on Wednesday that they will stay on Boeing's payroll until Jan. 17, to comply with federal requirements to notify employees at least 60 days prior to ending their employment.

News that Boeing would send out the Worker Adjustment and Retraining Notification (WARN) in mid-November was widely expected. Another round is expected in December. Boeing could also use workforce attrition, selective hiring and sales of subsidiaries to reduce workforce.

Boeing shares gained 2.6% to close at $143.87 on Monday. In October, Boeing's new CEO, Kelly Ortberg, said the company does not intend to "take people off production or out of the engineering labs." Industry-watchers have been waiting for the WARNs for some indication of how the layoffs could affect workers in the company's key manufacturing hubs. However, several hundred engineers and production workers were among those who received pink slips last week.

The Society of Professional Engineering Employees in Aerospace said 438 of the union's members at Boeing received layoff notices last week, including 218 engineers and 220 technicians.

The International Association of Machinists and Aerospace Workers (IAM) District Lodge 837 in St. Louis said Boeing sent notices to 111 members, most of whom made wing components for the 777X.

Who is being laid off seems to vary between sections within Boeing, several non-union workers who received WARNs told Reuters.

One engineer in Boeing Defense, Space & Security said all but two or three members of his 12-person team were let go, while another said she was the only one of her roughly 20-person team to receive a WARN. Both said they provide vital support for production and design engineers, but they are not considered to work in production. The notices come as Boeing tries to restart production of its strongest-selling 737 MAX, after a weeks-long strike by more than 33,000 U.S. West Coast workers halted output of most of its commercial jets.

(Reporting by Allison Lampert in Montreal, Dan Catchpole in Seattle and Shivansh Tiwary in Bengaluru; Editing by Daniel Wallis, Shilpi Majumdar and Matthew Lewis)