At first glance, it looked like so many other photos posted on social media, the kind taken by excited travelers en route. The wing of a plane, juxtaposed against fluffy white clouds, with the sun streaming through. The caption read: “U.S.A. here we go.”

On board that August flight from Jakarta to Los Angeles were Kaesang Pangarep, the younger son of President Joko Widodo of Indonesia, and Mr. Kaesang’s wife, Erina Gudono. Details of the trip trickled out on Ms. Erina’s social media accounts: a $1,500 stroller for their soon-to-be-born baby and a $25 lobster roll for lunch. Her posts were seen as tone deaf and led to an uproar at home because most Indonesians cannot afford luxury items.

But what made many furious was the fact that the couple traveled on a private jet. It was the antithesis of the Everyman image Mr. Joko has long projected. The plane was linked to Shopee, the operator of an online mall. The company had planned to construct a new building in the city of Solo, where Mr. Joko began his political career and where until recently the mayor was his older son, Gibran Rakabuming Raka.

“If Kaesang wasn’t the mayor’s brother who had signed an agreement with Shopee, would he really have been able to fly on Shopee’s private jet?” said Boyamin Saiman, the coordinator of the Indonesian Anti-Corruption Community, a watchdog group, which filed a complaint over the matter.

Mr. Kaesang has denied wrongdoing, saying he “hitchhiked” on a friend’s plane while not disclosing who the friend is.

The nation’s graft-fighting body, the Corruption Eradication Commission, is now investigating whether the flight constituted a bribe. The probe is still undergoing an “internal administration process,” according to a spokesman from the commission. It’s unclear who owns the jet now, but it was once the property of Garena Online, which has the same corporate parent as Shopee: Singapore-based SEA Limited. Garena did not respond to a request for comment.

The New York Times