(CNN) Alabama teens Janizia and Raven have been dating since September and talking about prom since December.

To make it memorable for her girlfriend, Janizia decided to stage a " promposal " -- the act of inviting someone to prom in an elaborate fashion, often involving props and flash mobs.

Janizia went forward with her plan at Alexandria High School's annual talent show on January 30. After Raven performed a rendition of Kehlani's "Honey," Janizia stepped forward with a poster asking the question "Prom?" on a rainbow background.

Raven nodded yes and some in the audience cheered, Lambda Legal attorney Paul D. Castillo said. He asked that the minor teens be identified only by their first names, out of concern for their safety.

What happened next left the girls and their parents questioning whether the school will let them go to prom, Castillo said.

A just punishment?

Janizia received one day of in-school detention for the promposal, the lawyer said. The girls and their families worried that the disciplinary action could be a reason to prevent Janizia from attending prom with Raven. So Lambda Legal sent a letter to the Calhoun County School District on their behalf seeking written assurances that they will be able to attend the March 10 dance together -- and threatening legal action if they didn't receive them by February 14.

Principal Mack Holley told the Anniston Star newspaper that Janizia was only disciplined because it's against school rules to do promposals at school events, and that she had been warned not to do it. Holley did not respond to CNN's request for comment.

But Holley's behavior after the promposal suggests there were other motives, Castillo said.

'Pray for me during these trying times'

The letter says Holley admonished the couple the next day over the school's public announcement system. He said "this is a Christian school" with "Christian values" and apologized to "anyone who was offended" by the promposal, the letter says.

He asked the school community to "pray for me during these trying times," according to the letter.

The sign Janizia used in her promposal.

The letter demands an apology from the district for what it describes as discriminatory treatment that violated Janizia's rights. It asks that the district expunge any disciplinary action related to the promposal from her record and clarify in writing that it will not tolerate mistreatment of LGBT students.

"Janizia is an honor student, an athlete, and she is a lesbian. I'm proud of all of those things, and I am offended and hurt as a woman of faith that the Principal would try to use Christianity as a reason to treat my child different from any other child at school," Jeanise, Janizia's mom, said in an email. "My daughter and her girlfriend should be able to go to prom like any other student."

The district declined to comment on the letter and referred CNN to a previous statement on its website, in which it said legal constraints prohibited it from discussing student disciplinary actions. The statement said that recent published reports created a "misimpression regarding the school's rationale in responding to the situation in question."

"Students, parents, and the public may be assured that the Calhoun County Board of Education remains firmly committed to guaranteeing its students equal educational opportunities in all phases of school administration, including student discipline," the statement said.

"Our investigation to date confirms that school officials have fully honored that commitment in this instance. The faculty and staff at Alexandria High School -- and at all Calhoun County Schools -- strive daily to provide a nurturing, fair, and orderly school environment that is conducive to learning for all students, and will continue to do so. Should any evidence come to light that suggests a departure from that standard in this or any other instance, appropriate remedial action will be promptly taken," the statement said.

'It's abhorrent'

So far, the girls have heard nothing from the school directly -- another reason for the letter, Castillo said.

Holley told the local newspaper that the teens can't be banned from prom just for being a same-sex couple. "It's probably against the law," he said.

"Our clients deserve clarity on the issue," Castillo said. "They shouldn't have to worry at the eleventh hour whether they will be let in."

At least one former student has stood up for the teens. In a Facebook post after the news broke, Hunter Borders said he proposed marriage to his current wife at a previous talent show and didn't face discipline.

"Regardless of the intentions of the punishment, whether discriminatory or not, they are unnecessary. Nothing inappropriate took place. The event continued on, I'm sure, and if there was no kissing or anything similar then I feel the school should do what our tax dollars pay them do. Teach and let kids be kids," Borders said.

'We just want to go to prom'

Janizia said the ordeal has put a damper on what should be memorable time in their lives.

"Since I began dating Raven, I have been looking forward to our prom night," she said. "We have been looking for the perfect dresses, and even though she is my girlfriend, I was excited to have a special way to ask her to go to the dance with me. I thought this would be a memory we would cherish forever, but I was humiliated by the way we were singled out and that I was disciplined. We just want to go to prom and be treated like everyone else."

The letter notes that, before the promposal, a teacher advised Janizia to do it offstage to avoid possible ridicule. Then another teacher helped her hide the poster so she could show it. Then, at the talent show, the emcee asked Raven onstage after her performance, catching Janizia off guard.

The letter accuses the principal of continuing to unfairly single out the students after the promposal. The letter accuses Holley of pulling Janizia from detention on February 1 and asking her if she had contact with the media. Since then, Holley regularly visits their classrooms and follows them in between classes, the letter says.

Castillo said the case shows that the rights of LGBT people are still under threat, despite marriage equality and other advancements in recent years.

"Even though we have achieved victory after victory in the courts, LGBT people continue to suffer discrimination on a daily basis," Castillo said in an email. "It's no surprise that the climate continues to worsen in many places across the country when the President continues to erode protections for LGBT people in every facet of life while promoting religious-based discrimination in his policies. It's abhorrent."