Poland is invoking Article 4 of the NATO treaty after a number of Russian drones entered its airspace and were shot down Tuesday evening.

Polish F-16 fighter jets, Dutch F-35s, Italian AWACS surveillance planes and NATO mid-air refuelling aircraft scrambled to shoot down the drones. A NATO spokesperson said it was the first time the alliance confronted a potential threat in its airspace.

Here’s what we know so far, what it means to invoke Article 4, the potential for invoking Article 5 and more.

What’s happening in Poland?

Poland said a significant number of Russian drones violated its airspace during a wave of Russian strikes on Ukraine. Polish authorities said 19 violations were recorded over seven hours, and nine crash sites were found, with some of them hundreds of kilometres from the border.

European leaders called the incursions a deliberate provocation by Russia. The incursions and the NATO response raised fears that the war in Ukraine could spill over.

NATO chief Mark Rutte said that a full assessment of the incident had not yet been made but added that, “whether it was intentionally or not, it is absolutely reckless, it is absolutely dangerous.”

Russia’s Defence Ministry said its drones had carried out an attack on military facilities in western Ukraine but that it had not planned to hit any targets in Poland.

What is NATO?

NATO stands for the North Atlantic Treaty Organization, an alliance of 32 countries from Europe and North America, including Canada, that is founded on the principle of collective defence. In other words, if one NATO ally is attacked, then all NATO allies are attacked.

The alliance was created in 1949 with the U.S. military as its powerful mainstay, essentially to counter the Soviet Union and its eastern bloc satellites during the Cold War.

What is Article 4 of the NATO treaty?

Article 4 of the NATO treaty’s 14 articles calls for member states to consult whenever “the territorial integrity, political independence or security” of a member is threatened.

Under Article 4, members can bring any issue of concern – especially related to the security of a member country – to the table for discussion with the North Atlantic Council (or NATO’s principal political decision-making body). The alliance also says that all decisions are made by consensus, after discussion and consultation among member countries.

Article 4 has been invoked only seven other times in the 76-year history of the alliance, most recently in 2022, when Bulgaria, the Czech Republic, Estonia, Latvia, Lithuania, Poland, Romania and Slovakia called for consultations after the start of Russia’s full-scale invasion of Ukraine.

Poland says it shot down drones that entered its airspace on Wednesday, with the NATO member calling the incursion “an act of aggression.” It marks the first time a member of the alliance has fired shots in the war.

Reuters

What is Article 5 of the NATO treaty?

If Russia were determined to have attacked the territory of a member state, the focus would then shift to Article 5, the cornerstone of the founding treaty of NATO.

The charter stipulates that “the Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all.”

“They agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defense recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area,” it says.

Tusk described Russia’s action as ‘a large-scale provocation,’ carried out during a wave of Russian strikes on Ukraine. The drones were shot down over Poland’s territory with help from NATO allies.

The Associated Press

How could the Ukraine-Russia war trigger Article 5?

Since Ukraine is not part of NATO, Russia’s full-scale invasion in February 2022 did not trigger Article 5, though the United States and other member states rushed to provide military and diplomatic assistance to Kyiv.

However, experts have long warned of the potential for a spillover to neighbouring countries on NATO’s eastern flank that could force the alliance to respond militarily.

Such action by Russia, either intentional or accidental, has raised the risk of widening the war by drawing other countries directly into the conflict.

Is invoking Article 5 automatic?

No. Following an attack on a member state, the other members come together to determine whether they agree to regard it as an Article 5 situation.

There is no time limit on how long such consultations could take, and experts say the language is flexible enough to allow each member to decide how far to go in responding to armed aggression against another.

Article 5 has been activated once before – on behalf of the United States, in response to the Sept. 11, 2001, hijacked-plane attacks on New York and Washington.

Foreign Affairs Minister Anita Anand and Defence Minister David McGuinty say Canada will support Poland after Russian drones violated NATO airspace overnight.

The Canadian Press

What does the incursion mean for the rest of Europe?

The Sept. 10 incursion has caused alarm in capitals across Europe, where there have long been fears of an escalation of Russia’s invasion of Ukraine.

“The Russian war of aggression against Ukraine poses a threat to the security of all of Europe,” said Swedish Prime Minister Ulf Kristersson. “Poland has every right to defend its airspace. We give our full support to Poland, as a NATO ally and EU member. Sweden and Poland stand united in our support for Ukraine.”

British Prime Minister Keir Starmer called the drone incursions an “egregious and unprecedented violation of Polish and NATO airspace.”

Ukrainian President Volodymyr Zelensky said that at least eight Russian drones had targeted Poland during Wednesday’s raid, which involved some 415 drones and more than 40 cruise and ballistic missiles. One person was killed in Ukraine and three others were reported injured so far, he added.

The attack was “an extremely dangerous precedent for Europe,” Mr. Zelensky added.

What is the response from Canada?

Prime Minister Mark Carney called Russia’s incursion “reckless and escalatory” in a post on X Wednesday morning, adding that Canada stands with Poland and NATO allies.

“We are closely coordinating with them, and we will remain vigilant against Russia’s attempts to widen and prolong the conflict with Ukraine,” he said.

Russia’s incursion into Polish airspace last night was reckless and escalatory. Canada stands with Poland and our NATO Allies. We are closely coordinating with them, and we will remain vigilant against Russia’s attempts to widen and prolong the conflict with Ukraine.

— Prime Minister of Canada (@CanadianPM) September 10, 2025

Foreign Affairs Minister Anita Anand also condemned the attack in a post on X Wednesday morning.

“Overnight, Russian drones violated Polish, and NATO, airspace during an attack against Ukraine. Yet another horrendous example of Putin’s refusal to seek peace,” she wrote. “Without question, Canada stands in full solidarity with Poland and Ukraine. We continue to call on Russia to put an end to its unjustified and illegal war.”

Overnight, Russian drones violated Polish, and NATO, airspace during an attack against Ukraine. Yet another horrendous example of Putin’s refusal to seek peace.

Without question, Canada stands in full solidarity with Poland and Ukraine. We continue to call on Russia to put an…

— Anita Anand (@AnitaAnandMP) September 10, 2025

With reports from Paul Waldie, Mark MacKinnon, Reuters and the Associated Press.