You are making this way more complicated than it needs to be. People need to be understood by the people they are talking to. There's no "correct accent", just whatever makes you understood by the other party.

but if this was official feedback then it seems to be in violation of Title VII of the Civil Rights Act.

Not in the fucking slightest and it's actually making me angry that you would imply "you need to be understandable" is in any way equivalent to

constantly made fun of their accents, ordering them to speak English even when they were already speaking in English. Some Filipino-American workers endured humiliating threats of arrest if they did not speak English and were told to go back to the Philippines. In a particularly offensive incident, an employee sprayed air freshener on a claimant's lunch due to the offender's self-professed hatred of Filipino food.

and

subjected to explicit and graphic commentary about their body parts by their supervisor; spreading rumors about their purported sexual activities; spying on them as they attempted to use portable toilets; engaging in sexual bantering and joking regarding the women with certain male harvesters.

If no one knows what the fuck you're saying, it's impossible to do your job. That's all.