The prolonged grounding of Boeing Co.’s 737 MAX aircraft is rippling through the U.S. economy, hurting the nation’s trade balance and clouding the outlook for airlines, suppliers and their tens of thousands of workers.

Companies ranging from American Airlines Group Inc., to engine maker General Electric Co. and smaller parts suppliers have cited the grounding and halt in deliveries of the jetliner for financial damage or the suspension of profit guidance. Several U.S. and foreign airlines are cutting back on routes and capacity...