Story highlights Democrats in the Missouri state Senate began their filibuster Monday

They say the proposed measure discriminates against same-sex couples

Supporters of the bill say it promotes religious freedom

(CNN) With a marathon filibuster session on the floor of the Missouri Senate, Democratic lawmakers are trying to block a measure they say discriminates against same-sex couples.

Senate Joint Resolution 39 , dubbed by its supporters as a "religious freedom" bill, proposes an amendment to the state's constitution over the "protection of certain religious organizations and individuals from being penalized by the state because of their sincere religious beliefs or practices concerning marriage between two persons of the same sex."

"This bill is a direct hit on those individuals who decide to love and be in love with the same sex, and that's not fair," said Sen. Jamilah Nasheed, one of eight Democratic state senators trying to stop the bill from passing.

The bill's sponsor told CNN it has a narrow focus.

"We spent a lot of time writing it to avoid the controversies we've seen in other states," Republican Sen. Bob Onder said.