Spirit AeroSystems, a key supplier to Boeing, shut down its factory in Wichita, Kansas, on Thursday after workers represented by the International Association of Machinists and Aerospace Workers voted to strike.

The suspended production comes after employees voted down Spirit AeroSystems' "best and final offer" and then authorized a strike, according to the union. The work stoppage is set to begin on Saturday.

The International Association of Machinists and Aerospace Workers, or IAM, represents about 6,000 workers at the plant.

"The IAM's dedicated and hardworking membership at Spirit AeroSystems has worked without fail during tumultuous times, including a pandemic that saw everything grind to a halt. Most of our members have concluded that the company's offer is unacceptable," the union said in a statement late Wednesday.

In response, Spirit AeroSystems said IAM-represented employees should not report to work on Thursday morning but will receive pay.

"We are disappointed that our employees represented by the IAM rejected our four-year contract offer and voted to strike. We believe that our fair and competitive offer recognizes the contributions of our employees and ensures we can successfully meet increasing demand for aircraft from our customers," the company noted it its statement.

The two sides, which have been negotiating since May, had come to a tentative agreement last week. The proposed deal included a 34% pay increase, continued health insurance, a 14.7% increase in retirement benefits with a new 401k match, voluntary Sunday overtime, and increased time off, according to the union. But rank and file members voted down the contract Wednesday.