The NYPD has for the first time laid out rules for using social media during investigations — but critics say the guidelines raise questions about privacy issues.

The five-page memo issued by Police Commissioner Raymond Kelly in September says officers involved in probes involving social media may register their aliases with the department and use a department-issued laptop whose Internet-access card can’t be traced back to the NYPD.

Christopher Dunn, associate legal director for the New York Civil Liberties Union, said police work on the Internet is ripe for abuse.

“Electronic undercover work is fine,” Dunn said. “But we worry about the ease with the police can use deceit on the Internet to monitor private communications.

“Police infiltration of social media should be closely regulated.”

The NYPD memo comes as police have made headlines for how it uses and deals with the Internet.

It has defended, for instance, its surveillance of Muslims by noting much of the information it gathers is from publicly accessible web sites.

The memo says officers can use subpoenas, court orders or search warrants to obtain certain electronic evidence.