A Fool’s day prank tweet by a budget airline Thai Vietjet staff could lead to criminal charges following outrage by ultra-royalist who saw it as an insult to Thailand’s King Maha Vajiralongkorn.

Following a complaint filed by an activist lawyer, Police will decide whether to pursue a criminal case under strict “lese majeste” laws — which make defaming the monarchy punishable by up to 15 years in prison.

The management of the airline have since apologized after the April Fool’s Day post announcing a fake new route between the northern city of Nan and Munich in Germany.

In a statement, Thai VietJet said the airline did not condone the post and suspended two of its staff who were responsible for the prank. The tweet, which was deleted few hours after it went up on Friday, raised anger among ultra-royalists who called for a boycott and apology from the airline.

“As the executive of the airline, I would like to admit my fault for not taking enough care of my staff,” said the statement, which quoted Thai VietJet CEO Woranate Laprabang. “The airline would like to clarify that the executives did not approve or support the publication of such online content and ordered an immediate removal upon learning about the incident.”

The tweet which has #aprilfoolsday disclaimer at the bottom, was accompanied by an image of two cities with the text “New route: Nan to Munich, starting at 1,010 baht per trip” is interpreted by netizens as a mockery to His Majesty King Rama X who reportedly spends much of his time in Germany.

The civil aviation regulator also said Sunday it will summon the airline for questioning, though it did not specify topic of the discussion.