Tensions are rising in the Boeing strike after the planemaker filed a complaint against the union

• The Boeing strike is growing increasingly ill-tempered as both sides have filed NLRB complaints.
• Talks resumed on Monday but collapsed the following day.

Boeing filed a complaint on Thursday with the National Labor Relations Board against the union representing 33,000 of its workers.

Seattle-area members of the International Association of Machinists and Aerospace Workers have been on strike for four weeks. They walked out in September after rejecting a new pay deal from Boeing.

Negotiations between Boeing and the IAM fell apart on Tuesday, having restarted the previous day. Both sides have since filed charges with the NLRB, each saying the other is bargaining in bad faith.

Rising tensions are palpable, and a longer strike would continue to hurt Boeing.

Bank of America analyst Ron Epstein estimated that the strike is costing Boeing $50 million a day. The planemaker is also at risk of having its bonds downgraded to junk status by credit rating agencies.

Boeing has implemented cost-cutting measures like asking some staff to take a rolling furlough of one week every four weeks.

The union is asking for a 40% pay rise and hopes to win back a defined benefit pension that was replaced with a 401(k) in 2014 negotiations.

Boeing's first offer included a 25% pay rise but was overwhelmingly rejected by workers. Its second offer on September 23 was upped to 30%, plus increased 401(k) contributions, but the union accused Boeing of "a blatant show of disrespect."

It said Boeing used direct-dealing tactics by sharing the offer with the media while union leaders were still reviewing the details and that the planemaker didn't engage in discussions about it.

In a memo to employees last Friday, seen by Business Insider, CEO Kelly Ortberg said a resolution "stands as a priority for me" ahead of resuming discussions on Monday.

However, Boeing withdrew its second offer and said the union was making unreasonable demands.

"Given that position, further negotiations do not make sense at this point," Stephanie Pope, CEO of Boeing Commercial Airplanes, told employees in an email Tuesday.

Reinstating the pension plan remains a key issue for many on the picket line — but Boeing's chief negotiator, Mike Fitzsimmons, told The Seattle Times there is "no scenario" where this will happen.

In a statement shared with BI, Boeing said it remains committed to reaching a compromise.

"The union's public narrative is misleading and making it difficult to find a solution for our employees," it added.

IAM District 751 did not immediately respond to a request for comment from BI.

Do you work at Boeing? Reach out to this reporter at psyme@businessinsider.com