President Trump Sued for Shrinking Utah National Monument

President Trump overstepped his legal authority on Monday when he shrunk one of Utah's national monuments by more than half its size ... according to a slew of wilderness groups taking 45 to court.

According to a lawsuit, obtained by TMZ, Trump's controversial decision to strip 900,000 acres from Grand Staircase-Escalante National Monument is an attempt to reverse President Clinton's 1996 decision to create the Monument.

But the wilderness groups say Trump needs to bone up on the Antiquities Act. They say it only allows Presidents to CREATE national monuments, but does NOT authorize them to do away with national monuments.

Critics say Trump is merely opening up the land so miners and frackers can snatch it up. However, in announcing the sweeping change, the Prez said it should be up to Utah residents to decide whether the land is developed at all.