A coalition of Louisiana environmental groups is suing the state over a law they say violates their free speech rights by restricting them from sharing information about air quality.

On days of heavy pollution in Sulphur, a southwest Louisiana town surrounded by more than 16 industrial plants, Cynthia “Cindy” Robertson once flew a red flag outside her home so her community knew they faced health hazards from high levels of soot and other pollutants.

But she stopped flying the flag after Louisiana passed a law last May that threatened fines of up to $1 million for sharing information about air quality that did not meet strict standards.

On Thursday, Robertson’s group Micah 6:8 Mission and other Louisiana environmental organizations sued the state in federal court over the law they say restricts their free speech and undermines their ability to promote public health in heavily industrialized communities.