Robert and Mildred Tong claim officials violated their freedom of speech and religion.
The suit was filed Tuesday in federal court in Chicago.
They say they were treated unfairly when they sought to take part in a "Buy a Brick'' program to raise money for a tot lot.
The Tongs, who have three children, paid 50 dollars for a commemorative brick that was to include the phrase ``Jesus is the Cornerstone.'' The bricks were to be used to pave part of the playground.
A March 31 letter from the park district said it couldn't accept bricks that have a religious message.
A park district spokesman wasn't immediately available for comment.