An employer claims unlimited access to an employee's communications on a work device
The employer conflates ownership of the device with unlimited rights over all communications that pass through it. In general legal principles, the fact that a device belongs to the employer does not extinguish the employee's reasonable expectation of privacy, does not grant the employer the right to intercept communications without consent, and does not eliminate the protections of applicable data protection and communications privacy laws. Device ownership and communication privacy are distinct legal questions.
After you respond, they may push back with these arguments. Members get the full rebuttal for each.