The company called former co-workers, without me knowing, for references. My friends have messaged me about this - some being fairly upset. Considering they didn't ask me for references at this stage in the interview (so I could ask if it's ok first). It seems like a lack of trust on their side. The company is engaging in non-standard practice, which is a HUGE red flag. I would go back to them and ask them why they're doing this and ask them to stop unless you've given them the green light. I would separately message your friends and explain the situation. I'm sure they would understand. Ultimately, I would be wary of the company in question.