The federal memo also says the Mounties and Canada's spy and border agencies are "very concerned" about increased paperwork and delays now involved in obtaining such information.
The note analyzing the June court ruling's impact were released to The Canadian Press under the Access to Information Act.
Basic subscriber information includes a person's name, phone number and Internet Protocol address, but not the actual content of messages, or metadata such as time stamps and routing codes.
Before the Supreme Court decision, law-enforcement agencies submitted hundreds of thousands of warrantless requests for such data annually to telecommunications companies, and they complied in about 95 per cent of cases.
While some companies have since stopped routinely disclosing basic customer information without a warrant, the federal privacy commissioner says there appears to be wide variation in how the court ruling is being interpreted.
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