A letter from the organization’s executive director, Claire Guthrie Gastanaga, was sent to Christiansburg High School Principal Kevin Siers on Tuesday requesting the “precise rationale” for the school’s ban of Confederate symbols in its dress code and in the parking lot.

“It is important to understand that the school must have a reasonable basis for forecasting disruption for each of its policies that limit student free speech,” Gastanaga wrote.

The school’s dress code has barred Confederate symbols since 2002. But the school’s policy prohibiting the flag from vehicles in the parking lot didn’t take effect until this school year, following a summer of angst over the symbol in the wake of June’s killings of nine black churchgoers during a Bible study in Charleston, South Carolina.

On Sept. 17 about two dozen Christiansburg High school students were suspended for violating their school’s dress code in a defiant rally in support of the rebel flag.

Gastanaga wrote that the ACLU was requesting the reasons Siers has to believe that the presence of the symbol is likely to cause a substantial disruption of the educational process or the school environment in each instance.

“For example, even if the school has reason to believe that display of the confederate flag on clothing inside the school building is likely to cause a substantial disruption, it might not have reason to believe that display of the flag on vehicles in the parking lot would cause a similar disruption,” she wrote.

County school spokeswoman Brenda Drake confirmed that the letter was received Tuesday, but said she was unable to comment about it directly due to potential for litigation.

A request to interview Siers was denied. Drake said she was the spokesperson for this issue.

ACLU spokesman Bill Farrar wrote in an email that the organization’s potential next step will likely depend on Siers’ or the county school system’s response.