The 1st Circuit Court of Appeals has ruled that the Mass. Transit Authority violated free speech rights in refusing to carry advertisements supporting the legalization of marijuana.

The Massachusetts Bay Transportation Authority rejected three ads submitted by the group Change the Climate in 2000, claiming they encouraged children to smoke pot. The transit authority argued that it has the right to protect riders from offensive or illegal messages.

But the 1st U.S. Circuit Court of Appeals found Monday that the MBTA, a quasi-government agency, does not have the right to turn down ads based on its viewpoint. Doing so violates the First Amendment, the court ruled.

"MBTA advertising space is literally a billboard for the expression of opinions to citizens at large. As a government agency, they shouldn't have the right to pick and choose what opinions they allow to be advertised," said Harvey Schwartz, an attorney for Change the Climate.