In a move that will complicate US-Japanese relations, construction on a key American military base in the Land of the Rising Sun was ordered to end, after a local governor, with the support of left-wingers, made good on anti-militarist campaign promises.

Okinawa Governor Takeshi Onaga demanded builders suspend work at the US installation along the island’s northeastern coast, citing a series of environmental and public safety concerns.

Onaga had previously railed against the construction of the base during an electoral campaign last fall that led to him ousting the prefecture’s pro-US conservative Governor. Throughout his election bid, Onaga was buoyed by the support of communists.

US defense officials told the Guardian that the Okinawa base, which is slated to cost $8.6 billion, is crucial to the administration’s so-called “Pivot to Asia.” The policy calls on the US to establish more of a presence on the Eastern side of the Pacific rim to confront increases in Chinese military spending and activity, and North Korea’s nuclear ambitions.

As The Sentinel reported last December, however, Japanese communists have other plans for the base—scrapping it. The Okinawa prefecture was home to historic communist victories during the nation’s 2014 election. The party secured victories in all of the prefecture’s four single-seat districts running on a platform opposing construction of the US military base. Prior to that, the party hadn’t won a single-seat election for national Parliament since 1996.

Onaga garnered the support of the Communists after he promised to close the Pentagon’s Futenma airbase in central Okinawa. The installation is currently being relocated to the coast following protests from the local community. Anger toward the base’s ongoing operations stem from the rape and abduction of a 12-year-old girl by three US soldiers in 1995.

The move by Okinawa’s governor sets up a showdown with Japan’s conservative Prime Minister Shinzo Abe, who has been in lock-step agreement with the Obama administration’s basing plans. A spokesperson for the Abe government dismissed Onaga’s order against the base, saying, “We are going to continue with construction work without delay.”

Onaga responded by saying that if builders don’t immediately stop their work at the base, he will revoke construction permits.

The new location for Futenma threatens a nearby marine ecosystem, and one of the world’s few remaining populations of manatee-related dugongs, local officials told The Guardian, noting that construction efforts had already damaged the site’s coral reef system.

US officials have not shied away from the debate in Okinawa. Appearing on Japanese television in January, Robert Eldridge, the deputy assistant chief of staff of government and external affairs for the US Marine Corps, said that protests near the Futenma military base amount to “hate speech.”

Onaga responded to the comments with strong criticism for the US military.

“They are very far from being good neighbors,” he said. “I have serious doubts about what is at the root of such thinking.”