BOULDER — The University of Colorado on Friday announced that it will close the entire Boulder campus to visitors on April 20 in its continued efforts to squelch the 4/20 pot smoke-out that in recent years has drawn more than 10,000 people to the Norlin Quad.

The closure, though, has ignited concerns from the Boulder County chapter of the American Civil Liberties Union, which has requested that its state legal team review the legality of closing a public college campus.

CU spokesman Bronson Hilliard cited a Boulder campus rule — “Campus Use of University Facilities” — that allows the chancellor to restrict access to the campus because of weather, safety concerns or “disruption.” He said the 4/20 closure falls into the latter category.

“This is definitely a measure that is unique,” Hilliard said. “That should be a signal to people that we’re very serious about ending this event on our campus.”

Only CU students and employees will be allowed on the campus on April 20, and they will be required to show their Buff OneCard campus identification to authorities.

Norlin Quad also will be closed April 20 to everybody, including students. Hilliard said fish-based fertilizer will be dispersed over the quad that day.

“The gathering disrupts teaching and research right in the heart of the campus,” Chancellor Phil DiStefano said in a statement. “The size of the crowd has become unmanageable, and limits our faculty, staff and students from getting to class, entering buildings and doing their basic work. It needs to end.”

Those ticketed for trespassing could face up to six months in jail and a $750 fine — stiffer than penalties for being busted with small amounts of marijuana.

But Judd Golden, chairman of the Boulder County chapter of the ACLU, said he has serious concerns about CU’s tactics.

“It would seem as though this would make the young person wearing a tie-dye shirt on 4/20 more likely to be intercepted by police than somebody who walked on the campus with a coat and tie,” Golden said. “The likelihood of selective enforcement seems significant.”

CU police spokesman Ryan Huff said officers will not engage in profiling.

For those visitors who have tickets for CU events on April 20 from 9 a.m. to 6 p.m. or who are participants in academic meetings, symposia, conferences or other officially sanctioned activities, limited access to campus will be provided via a special registration program.

Visitors should check in at the CU-Boulder East Campus Administrative and Research Center at 3100 Marine St. They must register for this service at colorado.edu/april20 beginning at 8 a.m. Monday or by calling the CU information line at 303-492-4636.