The two monuments were created by Democrats Barack Obama and Bill Clinton under a century-old law that allows presidents to protect sites considered historically, geographically or culturally important.
In addition to Trump, the lawsuit also names Secretary of Interior Ryan Zinke and acting director of the Bureau of Land Management Brian Steed as defendants.
On Monday, Trump announced that his administration would reduce the size of two national monuments: Bears Ears and Grand Staircase-Escalante, each more than a million acres in size.
The reasoning behind the move is to designate as protected "the smallest area compatible with the protection of the objects of scientific or historic interest", and the proclamation also opens the newly public lands to "disposition under all laws relating to mineral and geothermal leasing; and location, entry, and patent under the mining laws". "All five tribes will be standing together united to defend Bears Ears", said Natalie Landreth, an attorney for the Native American Rights Fund, which believes the cut would violate the Antiquities Act.
The Outdoor Industry Association said the move would hurt the economy and jobs, two of Trump's declared priorities.
Trump's decision to scale back the size of those monuments marks the most aggressive presidential effort to roll back national monument protections in USA history. The details of that report will be released Tuesday, he said.
"These are federal lands, these are our lands, they're everyone's, they're not just one state's" lands", said Mary Hertert, protester.
The recommendation came as a result of an executive order Trump signed in April asking for a review of his predecessors' use of the Antiquities Act to designate federal lands as national monuments.
Zinke said his review looked at 150 monuments, with 27 getting the most scrutiny. "And the Antiquities Act was never meant to prevent, it was meant to protect".
In a statement Monday, NARF said: "President Trump's action to revoke and replace the Bears Ears National Monument is not only an attack on the five sovereign nations with deep ties to the Bears Ears region, it is a complete violation of the separation of powers enshrined in our Constitution".
Both parks, or monuments as they are called, are in the dramatic Southern Utah red rock country.
Bruce Adams, chairman of the San Juan County Commission is glad President Trump is considering shrinking monuments across the American West.