Thousands of teenagers across the US are celebrating a "Day of Purity" to promote sexual abstinence.
The organisation wants to encourage sexual abstinence before marriage
High school students are wearing white t-shirts and encourage classmates to remain virgins until they are married.
The conservative US Christian group Liberty Counsel, which organised the day, said US teenagers should make a "public demonstration" of purity.
It said the day offered teenagers a chance to stand in opposition to "a culture of moral decline".
Liberty Counsel, which says it works to promote "religious freedom, the sanctity of human life and the traditional family", said young Americans faced a daily barrage of sexual messages in contemporary culture.
It said the Day of Purity enabled teenagers to make their voices heard and become part of America's true "counter-culture".
"When the youth of America stand up for sexual purity they send a message to parents, churches, communities, legislators and the media that they want a different America," it said in a statement on its website.
It added it had chosen the day before St Valentine's Day to encourage "purity in dating relationships" until marriage.
US teenager Melissa Millis, who says she will wear a white t-shirt to promote the Day of Purity at her Michigan state school, told the Associated Press news agency she was tired of feeling pressurised.
''The way sex is talked about, it's so casual, like it's an everyday thing, like going to McDonald's," she said.
US President George W Bush has massively increased funding and support for the US sexual abstinence movement during his term in office.
Christian abstinence organisation True Love Waits says it has more than one million card-carrying young members.
However, critics say the programmes are unrealistic and leave teenagers exposed to pregnancy and sexual diseases.