How important are Medical Provider Networks (MPN) for employers in fighting unauthorized treatment? More important than ever. In a recent WCAB en banc decision issued on April 20, 2011, the WCAB made it clear that when there is a valid medical provider network (MPN), and the injured worker obtains treatment outside the MPN, the employer and carrier will not be liable for the costs of that treatment, and more importantly, those reports will be inadmissible.|