About 1,500 of American Apparel's factory workers in Los Angeles are to be dismissed after an immigration investigation, according to local reports.

The Los Angeles Times said the workers had been fired by the apparel producer and retailer following a government inspection of its factory in downtown LA earlier this year.

The probe found that about 1,600 American Apparel workers had no authorisation to work in the US, with another 200 showing discrepancies in their documentation.

Quoting company lawyer Peter Schey, the newspaper said that about 1,500 workers would be sacked during September, and that American Apparel was "very disappointed and disheartened" to lose the workers.

In a letter to the workers, it added, company founder and chief executive Dov Charney said he was "deeply saddened" to let the workers go.

"Many of you have been with me for so many years, and I just cry when I think that so many people will be leaving the company," he said.

"It is my belief that immigrants bring prosperity to any economy."

Charney added that any workers who managed to sort out their immigration status would be given priority treatment to find work with the company.

American Apparel had previously said that the loss of the workers would have little or no impact on productivity, thanks to the current economic downturn.

Representatives for the company could not be immediately reached for comment.