Boeing delivered 33 new aircraft to customers in September in spite of a labor strike of Seattle-area workers that has shuttered two major assembly plants, the company said Tuesday.

Boeing delivered fewer airplanes in September compared with recent months and past years, as it felt the first effects of the ongoing Machinists strike.

A machinist strike is now in its fourth week, halting work at Boeing's factories in the Seattle area. Boeing delivered 33 airplanes in September, six more than during the same period a year earlier, as the company and its customers keep an eye on the impact of a machinist strike,