A gala celebrating the 75th anniversary of the Golden Gate Bridge was interrupted by bridge workers on Sunday.

Members of the Golden Gate Bridge Labor Coalition, representing 19 unions, demonstrated outside the California Historical Society around 2:30 p.m., protesting a health care premium sharing plan that they say burdens members’ families with higher costs.

Click the picture for a gallery of the protest and the exhibit.

The exhibit, “A Wild Flight of the Imagination: The Story of the Golden Gate Bridge,” features rarely seen artwork, photographs and other memorabilia from the opening of the historic span 75 years ago. According to the California Historical Society’s website, visitors will “learn what life was like in the years just before the Bridge was constructed.”

Members of the labor coalition said in a statement that “No one likes to ruin a party, but how can you be holding a 75th anniversary event celebrating the Golden Gate Bridge while attacking the people that actually make the bridge run at the same time?”

“Our members have run out of patience with the gross unfairness and inequality of this situation,” labor coalition co-chair Alex Tonisson said.