Are you suggesting they are doing it in violation of some law? This law isn't even a law yet, it's a proposal. Obviously eavesdropping and storing data with a court order is a valid use case under the GDPR. The GDPR might help ensure authorities properly delete old data though. I'm hoping that's already sorted since I hope authorities like law enforcement comply with the GDPR.
There is nothing inherent about eavesdropping that would violate the GDPR.
