Southwest has blamed an 'unprecedented' number of canceled flights on a mechanics union - and the stock is tanking

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• Southwest Airlines on Wednesday blasted its mechanics union for hundreds of cancellations.
• The union hit back, accusing the carrier of scapegoating.
• Also on Wednesday, Southwest said the impact from the government shutdown could be triple what it previously warned.
• Goldman Sachs downgraded the stock to sell on Tuesday, citing margin pressures from the launch of Hawaii flights.
• Shares sank as much as 4% in early trading Wednesday. Follow trading in real-time here.

It's not been a good week for Southwest Airlines.

The carrier on Wednesday blasted a mechanics union for hundreds of cancellations in recent days, a level it's calling unprecedented.

"On Feb. 12, just days after our last negotiations session with AMFA, we experienced an unprecedented number of out-of-service aircraft in four specific maintenance locations despite no change in our maintenance programs, no changes in leadership, and no changes in our policies and procedures," chief operations officer Mike Van de Ven said in a statement.

"We are committed to operating a safe fleet, and every report is investigated, which is why we issued a notice to require an "all hands" response to get out-of-service aircraft back into the fleet serving our Customers."

This week alone, Southwest has canceled more than 600 flights, and delayed over 1000 others, according to FlightAware. It blamed those interruptions on a number of planes out of service that was more than double the usual 20. Last week, it declared an operations "emergency"

The mechanics union hit back, accusing the airline of using it as a scapegoat for other issues.

"For Southwest's leadership to connect the airline's self-declared "operational emergency" to collective bargaining negotiations is simply an attempt to divert attention away from the airline's safety issues," the 2,700-member organization said in a statement.

Shares of Southwest sank more than 4% in trading Wednesday morning, as a revenue guide-down for the first quarter of 2019 and a Wall Street downgrade also weighed on investors' minds.

Read more: Assigned seats on Southwest? Here's how a major change would set the company apart from other airlines

In a regulatory filing Wednesday morning, the airline said the government shutdown would have more of an impact than the previously disclosed $10 to 15 million. It now expects a negative revenue impact of $60 million due to "softness in passenger demand and bookings as a result of the government shutdown."

Separately, a downgrade from Goldman Sachs related to its Hawaii launch was also adding to the airline's headache. Analyst Catherine O'Brien cut her rating to sell for the stock, saying the new routes could shrink Southwest's pretax margins by 60 basis points.

"We continue to be positive on LUV's long-term thesis, but we prefer ALK at this time," she said in a note to clients Tuesday evening.