There may an unfair labor practice or two at work here.
What are the written standards in place for requiring a breathalyzer test? Are those standards available to all employees at any time, before the fact? Is the machine tested and certified? Is the person performing the tested trained and certified? What are the laws and regulation in place in allowing employers to perform such tests? Have the employees signed off on allowing these tests as a condition of employment?
So what happens if your friend just emerged from the bathroom and had gargled mouthwash? Or perhaps they have an unknown medical condition that might be perceived by others as alcohol on the breath on occasion?
Even if you live and work in an at will state, you do have employee rights. The real question is are you willing to fight for them in a potential adverse action, or be bullied by an employer into submission? Face it, in this jobs economy I would do my best as an employee to keep my job, and that includes being sharp on the job as well as being ready to fight for the job (if it’s worth it) when accused I haven’t been sharp on the job.