Labour legislator Tom Watson and Conservative David Davis say there are not enough safeguards against "arbitrary, disproportionate or abusive retention and use of personal data."
They are asking judges to find the Data Retention and Investigatory Powers Act rushed through Parliament last year in breach of privacy protections in the European Convention on Human Rights.
The law requires communications companies to retain call and search records for 12 months for possible investigation. The government says police or security agencies need a warrant to access the content of calls or emails.