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OMAHA, Neb. — An elementary school principal in Omaha, Nebraska is on administrative leave after asking teachers to not celebrate Christmas in classrooms.

An internal memo, signed by Principal Jennifer Sinclair as “The (Unintentional) Grinch who stole Christmas (from Manchester),” included a list of Christmas-related items and activities that could not be used in class at Manchester Elementary School.

“I will do my best to communicate the expectation from here on out, which aligns with my interpretation of our expectations as a public school who seeks to be inclusive and culturally sensitive to all of our students,” Sinclair said in the memo following a list of “not acceptable” practices like the following:

Using images of Santas or Christmas items on worksheets.

Trees in classrooms.

Elf on the shelf.

Singing carols.

Playing Christmas music.

Sending a scholastic book that’s also a Christmas book.

Making ornaments as gifts.

Reindeer.

Christmas videos/movies and/or characters from Christmas movies.

And a most curious “not acceptable” item: candy canes.

According to Sinclair, the shape of a candy cane and its color strongly represent Christianity and Catholicism.

“Historically, the shape is a ‘J’ for Jesus. The red is for the blood of Christ, and the white is a symbol of his resurrection. This will also include different colored candy canes,” Sinclair wrote.

The memo was obtained by nonprofit Christian ministry Liberty Counsel, which sent a letter urging the school district to reverse the ban, saying it violates the US Constitution by showing hostility toward Christianity.

“We sent a demand letter to the Elkhorn School District last Friday demanding a response by close of business this past Monday. The School District attorney responded and advised that the action of Principal Sinclair was contrary to school district policy,” Mat Staver, Founder and Chairman of Liberty Counsel, told CNN.

“While we did not ask for Principal Sinclair to be placed on administrative leave, we did believe she should apologize and that the situation be corrected immediately.”

On Wednesday, Sinclair sent out an email to parents apologizing for any confusion, CNN affiliate WOWT reported.

“Last week, in an attempt to provide clarity, I mistakenly sent out an internal staff memo detailing what can and cannot be done in a public school surrounding the holiday season,” said the email, which was shared to WOWT by a parent.

“I wanted to reach out and make sure our families understand what occurred, and what has been done to correct the issue. I understand that the information I initially provide was incorrect and I sincerely apologize for any confusion or concern this has caused and the negative attention this issue brings to the District and Manchester.”

Kara Perchal, spokeswoman for the school district, said Sinclair has not released any other comments, and as of Thursday she has been placed on administrative leave.

“Principal Sinclair was in her first year as an employee at Elkhorn Public Schools,” Perchal told CNN. “Due to the fact that this is an ongoing personnel issue, the district cannot comment further.”

In a statement sent by Perchal, the Elkhorn School District said no other schools have reported similar issues.

“Elkhorn Public Schools District administration promptly addressed the issue at Manchester Elementary School regarding the memo that was sent by the principal to Manchester elementary staff. The memo does not reflect the policy of Elkhorn Public Schools regarding holiday symbols in the school. The district has since clarified expectations and provided further direction to staff in alignment with district policy. This issue was limited to Manchester Elementary School and did not arise at any other schools within the district,” the statement read.

CNN has not been able to reach Sinclair.