Mather joined a call with a Rotary Club earlier this month and spoke at length about his team ... and in parts of the conversation -- which surfaced on video over the weekend -- he made cracks about some of his players' and staffers' abilities to speak English.

When talking about Hisashi Iwakuma -- a former M's pitcher who just signed on to be a part of the Mariners' coaching staff -- Mather said, "Wonderful human being; his English was terrible."

Mather then brought up English-speaking abilities again later when discussing top minor league prospect Julio Rodriguez.

"Julio Rodriguez has got a personality bigger than all of you combined," Mather said. "He is loud. His English is not tremendous."

The MLBPA ripped Mather for the remarks ... saying in a scathing statement Monday the words were "highly disturbing" and "offensive."

For his part, Mather apologized vehemently in a statement of his own, saying, "There is no excuse for my behavior, and I take full responsibility for my terrible lapse in judgment."

Clearly, though, the mea culpa wasn't enough to save his job ... Mather resigned shortly after saying sorry -- with Mariners chairman John Stanton calling Mather's words inexcusable.

"There is no excuse for what was said," Stanton said, "and I won't try to make one. I offer my sincere apology on behalf of the club and my partners to our players and fans. We must be, and do, better."