An October 10 letter from the American Civil Liberties Union to the Boulder Valley School District Board of Education asks the school to cease the practice.
A school district spokesperson says the cell phone text message searches conducted by administrators are perfectly legal.
"They checked with our legal affairs office every step of the way," said Briggs Gamblin.
The ACLU claims the searches began last spring when a student was accused of smoking in a school parking lot. When a search of the student's bag and pockets didn't turn up any evidence, a principal took the student's cell phone and logged its text messages.
The school district will not say what administrators will looking for or what they found, because they maintain it is an internal school discipline issue.
Parents tell the ACLU that the text message logs have been put in students' permanent disciplinary files.
Mark Silverstein, legal director of the Colorado ACLU, says the incidents at Monarch don't meet the Fourth Amendment's standard of "reasonable" searches and seizures.
"There's a big difference between a search of pockets or a backpack and a search of cell phones," Silverstein said.
"It's just not right," according to Monarch senior Dylan Hayward.
Hayward told 9NEWS he would not want administrators searching his cell phone because of personal messages he receives from his mother.
"She lets me know about family affairs, Grandma's surgery and stuff like that," Hayward said. "I don't want everyone going through my texts and learning about my problems and stuff like that... It's not cool."
Silverstein calls that information, "personal and private evidence that has absolutely no relevance to the original objective of the search."
The school district is standing by its searches saying it balances the civil liberties of students with the responsibility to ensure safety.
Both sides have expressed interest in sitting down to discuss the issue.
