The Can't Stop the Feeling singer took to Instagram and posted a selfie from a polling booth in Memphis, where he was casting his vote early for the upcoming presidential election, to encourage his 37 million followers to get involved in the Trump v Clinton clash.

His act of civic duty and subsequent PR campaign for the Rock The Vote movement - a not-for-profit organisation that aims to mobilise young voters in the United States - has the potential to land him a short stint in jail or a fine.

Since May 2015 it has been illegal to take photos or video in voting booths in Tennessee.

Last year governor Bill Haslam passed a statewide bill stating that mobile phones must only be used inside polling stations for "informal purposes to assist the voter in making election decisions".

Timberlake - husband of 7th Heaven star Jessica Biel - could face a potential $65 fine or 30 days behind bars.

However the photo he took inside the New Bethel Missionary Baptist church in Shelby County, where every polling site has signs stating what can and cannot be done with a phone, is just being scrutinised, not investigated.

A spokesperson from the Shelby County Districy Attorney General's office retracted an earlier comment that the singer's selfie was being reviewed for a possible violation of state election law.

"While we are aware of an allegation that someone may have violated a Tennessee state election law, we have not been presented anything by an investigative authority," communication director Vince Higgins told The Commercial Appeal.

The Tennessee Secretary of State's office saw the funny side and released a pun-laden statement to remind residents to vote either on November 8 or earlier.

"We're thrilled Justin can't stop the feeling when it comes to voting so much that he voted early in person and is promoting voting to his millions of fans," spokesman Adam Ghassemi said, riffing off Timberlake's latest song title.

"In Tennessee, using electronic devices inside polling locations to take pictures, videos or make calls is not allowed. We hope this encourages more people than ever to vote, but Tennesseans should only use their phones inside polling locations for informational purposes to assist while voting."

It is not illegal for Australian voters to take selfies while voting, according to the Australian Electoral Commission.