Taiwan convened a National Security Council meeting this week and lodged a high-level formal protest with Beijing after China opened four new civilian flight paths over the Straits of Taiwan without warning and immediately filled them with civilian airliners.

Voice of America relates accusations from Taiwanese officials that China’s action violates agreements on air traffic reached in 2015, and was taken as part of China’s campaign to ratchet up political pressure against Taiwan.

“This is something China did unilaterally. It wasn’t something that was done through negotiation. It wasn’t something that people talked about or reached a compromise or consensus on,” explained Raymond Wu of Taiwan-based risk consulting firm e-telligence.

“They keep pushing the envelope. They are pushing Taiwan into a corner. They are hoping Taiwan will react or even overreact,” Taiwanese lawmaker Lo Chih-cheng complained. He expressed concerns that the world is too preoccupied with North Korea and securing Chinese cooperation to resolve its nuclear missile crisis to take note of China’s provocations against Taiwan.

The flight paths employed by China were mapped out in 2015, but China promised only limited use of one route and said the others would not be employed without further negotiations with Taiwan. There was speculation at the time that China announced the air routes without consultation or negotiation as a gesture of contempt for Taiwanese authority. The Taiwanese were informed the flight paths would be used on January 4, a matter of hours before Chinese aircraft began flying through them.

Taiwan’s Foreign Ministry said China’s actions “severely influenced regional security and flight safety,” although the move was carefully calibrated to be more of an insult or annoyance than a threat; no Taiwanese aircraft had to be rerouted and there are no immediate military ramifications. The air routes push close enough to Taiwan to seem aggressive without qualifying as a blatant invasion of Taiwan’s airspace.

When the routes were mapped in 2015, the announcement was seen as a humiliation of Taiwanese President Ma Ying-jeou; now the activation of those routes is seen as a comparable insult to his successor, President Tsai Ing-wen, who is much less amenable to Chinese demands than Ma.

Shortly after the routes were activated last week, Taiwanese Mainland Affairs Council Minister Chang Hsiao-yueh called China’s move “unacceptable, particularly if China intended to exert political pressure on Taiwan and impose a military threat under the guise of initiating new flight routes,” as reported by Channel NewsAsia. China’s Civil Aviation Administration said the routes were opened merely to relieve congested air traffic and enhance air safety.