Congress earlier this month passed legislation requiring the words "In God We Trust" as well as the Pledge of Allegiance to be etched into the walls of the cavernous complex, which sits underneath the Capitol building and greets thousands of tourists each day.
The Los Angeles Times, however, reports that the Freedom From Religion Foundation, a Wisconsin-based association of atheists and agnostics, has filed a federal lawsuit to stop the engraving.
The group argues the engraving would be unconstitutional because it would "give actual and apparent government endorsement and advancement of religion," while excluding nonreligious Americans.
"I was surprised that they would suggest that the national motto or the Pledge of Allegiance is unconstitutional," said Rep. Dan Lungren (R-Calif.), one of the sponsors of the legislation, according to the LA Times. "I think the historical significance is well established."
Lawmakers raised similar points in a letter sent to the architect of the Capitol before the visitor center was open, which read, "None of us should want to construct a $621 million shrine to political correctness that does not accurately reflect a significant part of American history."
The words "In God We Trust" were placed on U.S. coins during the Civil War era. However, the Freedom From Religion Foundation points out it was not placed on paper currency until the 1950's, during the Cold War. The words "under God" were inserted into the Pledge of Allegiance in 1954.
The engraving would cost as much as $100,000, the LA Times reported.