(Reuters) -A union representing more than 3,200 striking Boeing workers who assemble fighter jets and munitions said on Friday it and the company had agreed to resume contract discussions with help from a federal mediator next week.

The announcement came one day after the union filed an unfair labor practice charge with the National Labor Relations Board, accusing the company of not negotiating in good faith. 

The 75-day-long strike has delayed deliveries of F-15EX fighters to the U.S. Air Force, General Kenneth Wilsbach told the Senate Armed Services Committee in comments submitted for his October 9 hearing on his nomination as the Air Force's chief of staff.

AIR FORCE OPERATIONS AFFECTED

The delayed F-15 deliveries "will impact" operations at the USAF's Portland Air National Guard Base, and delay the modernized fighter's first deployment overseas next year, he said in written comments.

Members of the International Association of Machinists and Aerospace Workers (IAM) District 837 went on strike on August 4, after rejecting Boeing's second four-year contract proposal. The members work at Boeing Defense facilities in the St. Louis area.

In September, they rejected a third offer with few differences from the previous offer. 

Boeing management has said the aerospace company will not significantly improve its offer, and rejected a contract proposed by IAM leadership and overwhelmingly approved by union members. Instead, the company has expanded its plans to hire replacement workers.

IAM officials and members previously told Reuters they think Boeing is bluffing, noting the necessary training and security clearances for new workers take as long as six months to get.

The planemaker's stance on negotiations has drawn criticism from some senators, including Democrat Ed Markey and Republican Josh Hawley, who, along with Senator Bernie Sanders of Vermont, slammed the company during a committee hearing earlier this month.