Ubolratana Rajakanya Sirivadhana Varnavadi relinquished her royal titles in 1972 when she married an American. (Bobby Yip/Reuters)

The elder sister of Thailand’s king was nominated Friday as a candidate for prime minister in upcoming elections, upending a tradition where the Thai monarchy was seen as apart from the politics and presenting a serious challenge to the ruling military junta.

It also tests the boundaries of Thailand’s law that makes any criticism of the monarchy a criminal offense.

The princess, Ubolratana Rajakanya Sirivadhana Varnavadi, has officially shed her royal titles. But she is still regarded in the public mind as a member of the royal family, and her entry into politics sets an unprecedented quandary for her opponents in the March elections.

In short: Can they criticize her without running afoul of Thailand’s laws? In a sign of the extreme sensitivity, three Thailand-based legal and political analysts declined to comment on her candidacy.

The 67-year-old elder sister of Thailand’s king was put forward by the Thai Raksa Chart Party of former prime minister Thaksin Shinawatra, who was ousted by the military more than a decade ago.

The surprise move is a major break in the established protocols of Thai politics. It effectively aligns the princess — and the Thai monarchy — with Thaksin’s popular political movement, widely seen as anti-royalist and deeply disliked by the powerful military.

Her nomination poses a serious threat to the dominance of Thailand’s military junta, which has ruled since 2014 and unseated forces close to Thaksin.

But it also was not welcomed by her brother, King Vajiralongkorn. A palace statement read on all Thai television networks called Ubolratana’s political aspirations “extremely inappropriate” and against the “nation’s traditions, customs and culture.”

“Involvement of a high-ranking member of the royal family in politics, in whatever way, is considered an act that defies the nation’s traditions, customs, and culture, and therefore is considered extremely inappropriate,” said the statement, according to a BBC translation.

The statement, however, did not appear to demand that she change her mind.

Ubolratana’s nomination must still be accepted by the Thai election commission. The princess relinquished her royal titles in 1972 when she married an American she met in college, and they later divorced in 1998.

In an Instagram post after her nomination was announced, she pointed out that she lives “as a commoner” and accepted the nomination to show her “rights and freedoms without any privileges above fellow Thai citizens under the constitution.”

Thailand is now led by the military, which ousted Thaksin in a coup in 2006 and later helped remove his sister, Yingluck Shinawatra, from the role of prime minister in 2014. Prayuth Chan-ocha, a retired Thai general and the current prime minister, has also put his candidacy forward, and will be running against Ubolratana.

Analysts say that the princess’s plunge into politics could mark one of the biggest shifts in the balance of Thai politics in generations. The election, which will be held March 24 after a series of delays, was thought to be a foregone conclusion that would strengthen the hand of the military junta.

But the monarchy could now be seen as effectively aligned with Thaksin’s populist political movement, and if Ubolratana is to become prime minister, it could also pave a path forward for the return of the Thaksin family to Thailand.

Both Thaksin and his sister, Yingluck, have lived overseas since their ouster to avoid imprisonment on corruption charges they say are politically motivated. Thaksin, a telecommunications billionaire, remains wildly popular outside Thailand’s cities, where he offered cheap medical care and debt relief.

Under Thailand’s sweeping lèse-majesté laws, which criminalize any criticism of the royal family, it is unclear what the scope and flavor of a campaign against the princess will look like. It is also likely to complicate any analysis or media coverage of the Thai election, as well.

Thailand’s monarchy is deeply revered in society and has always been seen as a stabilizing force in the country amid tumultuous political upheavals including bloody street protests and coups.

In theory, the royal protection laws only cover the king, queen and heir to throne. But in practice it has been more sweeping.

Ubolratana is the eldest child of King Bhumibol Adulyadej, who ruled from 1946 until his death in 2016. At the time of his death, he was the world’s longest ruling monarch.

The princess, seen as somewhat of a rebel for rescinding her privileges after her marriage to an American commoner, has earned somewhat of a celebrity status in Thailand. She lived in the United States with her husband, Peter Jensen, for over two decades, where she took the name Julie Jensen.

After their divorce, she continued to reside in the United States with her three children until they returned to Thailand in 2001. One of her children died in the 2004 Indian Ocean earthquake and tsunami the day after Christmas that killed hundreds of thousands.

She has adopted a more approachable persona than other members of the Thai royal family, and has appeared in pop concerts, singing Christmas carols and acting in movies.

Ubolratana’s political leanings, however, have been less clear. Rumors about her ties to the Shinawatra family have circulated in recent months, after she was pictured with Thaksin and Yingluck last year at the World Cup in Russia.

Her Instagram account, though private, has over 100,000 followers.