SAN ANTONIO - In a sudden blow to San Antonio's aerospace industry, Boeing San Antonio will announce Friday it's laying off as many as 600 workers at its Port San Antonio site because of a drop-off in commercial airline work, the manufacturer confirmed Thursday night.

Most of the affected employees will be workers employed directly by Boeing. The rest will be contractor employees, said Lorenzo Cortes, the company's communications manager for San Antonio. Boeing employees will be given 60-day notice on Friday.

The manufactuer's contractor employees will be released between Friday and sometime in May, Cortes said. As of Thursday, the Chicago-based Boeing Co. employed about 1,600 people, counting both direct workers and contractor employees, Cortes said.

"Current market conditions indicate we have an excess of workers," Cortes said. "If future projects come in, we foresee an increase in employment."

Boeing San Antonio cut 50 positions last September.

A city official warned at the time the number could have been a lot more. However, Boeing employees here recently were warned that more layoffs could be coming because of the completion of work on the KC-135 Stratotanker and United Airlines' fleet of 787 Dreamliners.

Boeing San Antonio started customizing Dreamliners in 2011, holding a huge ceremony in its Port San Antonio hangar in March that year to celebrate an upcoming series of other Dreamliners coming here.

On Thursday, the company had one Dreamliner in San Antonio, a refurbishment project not connected to a specific airline, Cortes said. After that, no further Dreamliners are expected, but the company continues to seek contracts from airlines, he said.

Port San Antonio CEO and President Bruce Miller said the Boeing layoffs are a temporary setback as the industrial park continues to transition to commercial projects as military contracts shrink from reduced U.S. Defense Department spending. "Boeing is an important part of the port's success and our community's future. We regret hearing about this workforce reduction and our thoughts are with the affected families," Miller said in a written statement. "Port San Antonio is proud to have Boeing among its original customers - a global standard-bearer with important opportunities around the world," he said.

A task force convened by Mayor Julián Castro last year recently produced a report titled "Port San Antonio Aerospace Strategy," which said the port should cut rents and prepare to undercut competing cities, states and regions for aircraft maintenance, repair and overhaul contracts. An action plan to follow up on the strategy is expected by June 30.