(Reuters) -Striking workers at Boeing Defense in the St. Louis area rejected the company's latest contract proposal on Sunday, sending a strike that has already delayed delivery of fighter jets and other programs into its 13th week.

In a statement after the vote, union leadership said the company had failed to address the needs of the roughly 3,200 members of the International Association of Machinists and Aerospace Workers (IAM) District 837.

The five-year offer was largely the same as ones previously rejected by union members. Boeing ( BA ) leadership has said repeatedly during the strike that the company will not significantly improve its offer.

In September, IAM members approved the union's proposed four-year contract. However, Boeing ( BA ) management has refused to consider the offer.

The IAM estimates that its offer would add about $50 million over the agreement's duration. Boeing ( BA ) CEO Kelly Ortberg is set to earn $22 million this year.