MILTON—Northstar Aerospace Canada Inc. says 135 workers at a manufacturing facility in Milton have launched a legal strike.

The company makes helicopter gears and transmissions and other machined and fabricated parts.

The workers, represented by CAW Local 112, walked off the job when their contract expired at midnight.

Northstar says changes sought are critical to the long term health of the Milton facility are critical as the industry faces volatile economic conditions, uncertain customer demand and reduced defense spending across the aerospace sector

The Chicago-based aerospace firm has plants in Chicago, Phoenix, Milton and Windsor.