Striking French train workers blocked passengers from boarding one of the few subways functioning in Paris on Monday, leading to a standoff with police on the 19th day of nationwide strikes over the government’s plans to raise the retirement age to 64.

The wildcat protest by a few dozen union activists caught passengers by surprise and spilled onto the streets around the historic Gare de Lyon train station, further disrupting a key travel hub after more than two weeks of transportation trouble around the country.

Images on French media and social media showed activists jumping and chanting and waving union flags as they moved through the subway station, engulfed in red smoke from the flares they were waving.