S&P Global Ratings said on Thursday if Boeing faces an extended worker strike, it could delay the planemaker's recovery and hurt its overall rating.

Boeing's U.S. West Coast factory workers started voting on Thursday on a much-criticized new contract and a possible strike, piling pressure on the company as it wrestles with chronic production delays and mounting debt.

A potential strike starting on Friday would be a big early blow to Boeing's newly appointed CEO Kelly Ortberg, who was brought on last month to restore faith in the planemaker after a door panel blew off a near-new 737 MAX jet in mid-air in January.

"A shorter strike (along the lines of the situation at Spirit Aero last summer where union leadership accepted the company's offer and membership rejected it) would probably be manageable for the company and the rating," said Ben Tsocanos, aerospace director, S&P Global Ratings.

Tsocanos said the strike could pressure Boeing's ability to reach its target of increasing MAX jet production to 38 planes a month by the end of the year.

S&P rates Boeing's long- and short-term issuer credit at "BBB-" and "A-3", respectively.