Google said the data collection was inadvertent and that it never used the information.
The Federal Communications Commission (FCC) investigated the incident and was unable to conclude whether Google violated wiretapping laws. But the FCC proposed a $25,000 fine because Google "deliberately impeded and delayed" the agency's investigation into the case.
The FCC said Google refused to hand over internal emails or identify employees. When questioned, one engineer invoked his Fifth Amendment right against self-incrimination in order not to testify.
A Google spokeswoman said the company disagrees with the "FCC’s characterization of our cooperation."
When the FCC announced its fine, Markey called it a "mere slap on the wrist" for Google, which brought in $38 billion in revenue last year.
Markey is one of the most senior Democrats on the Energy and Commerce Committee and is the former chairman of the subcommittee on Communications and Technology.