PARIS (AP) — Twenty-nine environmental activists were arrested Friday after breaking onto a runway of Paris’ Orly Airport to protest plane emissions — just hours after the airport reopened for the first time since the virus pandemic grounded most air travel three months ago.

The activists from Extinction Rebellion (XR) demanded that France’s domestic flights be immediately stopped because of the high carbon emissions they produce.

The protesters broke into the airfield at 10 a.m. after warning security guards of their presence, according to Franck, an XR activist on the scene who refused to give his full name for fear of retribution from authorities.

The activists set off flares of red smoke as they walked toward the runway to signal their presence to the surrounding planes. Several pairs of protesters locked themselves together by the neck to complicate their eventual arrest, Franck said.

About 30 minutes later, gendarmes arrived, and most of the activists were arrested or left, he told The Associated Press. Police said 29 people were detained. Franck said a journalist was among them.

One flight was delayed for a few hours, and others were redirected onto other runways, said an airport official who wasn't authorized to be publicly named. Other traffic wasn't affected, said the official, who added that the airport would press charges against the activists.

France’s finance minister called recently for reducing domestic air routes to encourage train travel instead, and environmental groups want the country to go even farther and ban all domestic air travel.