NEEDVILLE, Texas - Three civil rights advocacy groups have warned a Houston-area school district superintendent that his threat to punish students who disrupt classes to protest current gun laws may violate their constitutional free-speech rights.

In a statement issued Tuesday, the Texas ACLU, Texas Civil Rights Project and Texas Appleseed said they had sent a letter to Needville school district Superintendent Curtis Rhodes that expressed their concern over Rhodes' threat.

Texas ACLU staff attorney Kali Cohn said school administrators can't censor political speech nor punish students more harshly for missing school to participate in political protest than they would for any other unexcused absence.

Last week, Rhodes wrote to families that students would face a three-day, out-of-school suspension if they joined in growing protests nationwide over last week's school shooting in Florida.