The atheist group Freedom From Religion Foundation (FFRF) might think they've scored a victory when they caused the cancellation of a 25-year-old Christmas tradition held annually at The Grotto's Christmas Festival of Lights in Portland, Oregon.

However, the Christian residents of the area are not willing to let go off this tradition without a fight.

The Grotto's Christmas Festival of Lights, which is held yearly in a botanical garden and Catholic shrine in Portland, Oregon, features choirs from churches, schools, and other organisations.

It is a well-loved tradition cherished by locals. But the FFRF members did not like it, so they filed a complaint urging officials from the Portland Public Schools District to ban all school choirs from joining the event, the Oregonian reported.

"Just because it's a tradition doesn't mean it's legal. Whole generations of students in Portland are being sent the message that it's fine for public schools to promote Catholic events," FFRF co-president Annie Laurie Gaylor said.

When lawyers reviewed the atheist group's complaint, they agreed that the school district faces legal risks should they decide to continue the tradition. They agreed to put a stop to it, and teachers were informed about the decision just last month.

"It was a sad decision for us to make and it was a hard decision," the school district spokeswoman Christine Miles said. "If we know there is a legal risk and we don't do anything, then that's not the right thing to do."

But locals are not tolerating the complaint. In fact, one of the school's alumni has already created a petition on Change.org, urging authorities to reverse their decision to end their participation in the Grotto Christmas Festival of Lights.

"I attended Grant HS from 1991-1995. I was a member of the Acapella Choir and The Royal Blues," she wrote. "We had the honour of singing all over the state of Oregon and internationally as well. One of my favorite performances was our yearly concert at The Grotto. It became a tradition. It was never a Catholic tradition, it wasn't a religious tradition, it was a performance tradition. It was an opportunity for us to sing together and celebrate music! I feel that your decision was unnecessary and I hope you will reverse it!"

Within just 24 hours since the petition was put up, it already garnered 1,000 signatures.