Romania notified allies on Thursday that President Klaus Iohannis was considering challenging frontrunner Mark Rutte for the NATO top job.
Iohannis' last-minute move comes as the biggest powers in the 31-strong alliance already declared support for Rutte over the last 24 hours, with the U.S., the U.K., Germany and France all saying they back the outgoing Dutch prime minister as the next leader of NATO.
About 10 countries remain undecided, including some Eastern European nations who share strategic concerns with Russia-skeptic Romania, but they will find it difficult to openly challenge U.S. President Joe Biden's preferred candidate.
Two NATO diplomats with knowledge of the development confirmed the Romanian move to POLITICO. Bloomberg first reported Iohannis's potential challenge.
Romanian officials are not disputing the information.
"Through the missions of each member state, intentions [and] suggestions are informally transmitted to NATO," a government official told local media.
The Romanian presidential office declined a request for comment.
NATO officials fear that Iohannis' late entry could be seen as dividing the unity of the alliance, which is already facing threats from the potential return of Donald Trump as U.S. president. Trump has repeatedly vowed to weaken the collective defense stipulated by NATO.
But Eastern European countries are annoyed by what they see as Rutte's lack of incentive in reaching out to nations on the border with Russia.
Saying that they don't mean to stand in the way of Rutte, a senior Eastern European diplomat said: "At least somebody has to ask, 'OK, Mark, how are you going to deal with Russia?'"
They also point at Rutte's repeated failure in bringing the Dutch defense spending level up to the target of 2 percent of GDP agreed by all allies a decade ago, which they said could be used against him if Trump were to be elected.
That's in addition to the bilateral ill-feeling between the Netherlands and Romania, two NATO members who are part of the European Union, as Rutte's government for years refused Bucharest's entry into Schengen, the borderless zone for EU countries, citing the risks of corruption and criminal activities.