NATO Article 4

Article 4 of the North Atlantic Treaty, signed in Washington on 4 April 1949, says the allies will consult whenever any of them believes its territorial Integrity, political independence or security is threatened. Unlike Article 5, the collective-defence clause, it commits no ally to act.

Allies have invoked it nine times: Turkey five times between 2003 and 2020, Poland in 2014, eight eastern allies including Bulgaria in February 2022, and Poland and Estonia in September 2025. Warsaw's 2025 request followed about 20 Russian drones entering Polish airspace on 10 September, and NATO launched its Eastern Sentry air-defence mission within days.

Not every incursion leads to the clause. Romania found Russian drone debris on its soil repeatedly from 2023 without invoking it, and in 2025 changed its own law instead to let its forces shoot drones down.