Approximately 600 United Launch Alliance workers represented by the International Association of Machinists and Aerospace Workers (IAM) went on strike Monday morning following three weeks of unsuccessful contract negotiations. 

Citing concerns about travel, job security and subcontracting, union members voted Sunday to reject the company's final contract after their negotiating team recommended declining it. The strike began 12:01 a.m. Monday and involves ULA employees at three locations — Vandenberg Air Force Base, Cape Canaveral, Florida, and a manufacturing facility in Decatur, Alabama.

Union spokesperson Deirdre Kaniewski said 82 ULA employees at Vandenberg are represented by the union. The strike comes two days after the successful launch of NASA's Mars InSight mission from Vandenberg.

"Our members have spoken, and we honor their voice," Gary Allen, the union's western territory general vice president, said in a statement. "It’s now up to ULA to enhance their offer to meet the needs of these highly skilled workers."

The two parties had been at the bargaining table since April 16, with the final contract presented to members April 26. In a statement posted to its website, ULA called its offer fair, competitive and in the best interest of both ULA and its employees.

According to a summary of ULA's final contract, union members were offered a $350 cost of living increase; wage increases of 1.5, 1.75 and 2 percent each year of the three-year contract; a guarantee that no existing employee would be displaced due to subcontracting and a preservation of existing medical plans. Should the union opt to ratify the agreement by May 7, ULA would pay a $6,000 bonus per employee.

"We’re disappointed that the IAM members rejected ULA’s last, best and final offer and voted to strike," Tory Bruno, ULA president and chief executive officer, said in a statement. "We believe our proposed contract is very competitive with other companies. Importantly, ULA’s final offer contributes to ULA’s long term viability in an increasingly competitive launch business environment."

The company is currently implementing its strike contingency plans to meet its customer commitments, according to officials. All sites remain open and are not expected to be affected.

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Mathew Burciaga covers education in Santa Maria and the surrounding area for Lee Central Coast Newspapers. Follow him on Twitter @math_burciaga