GROTON — When the Groton-Dunstable Regional High School Chamber Chorus was booked for its second performance tour of Italy and Croatia, one of the highlights was an Easter performance at St. Anthony’s Basilica in Padua, Italy.

The basilica concert, where the group appeared in 2014, is now off. Prompted by a complaint by former Groton-Dunstable School Committee member Leslie Lathrop, lawyers for Americans United for Separation of Church and State in Washington, D.C. contacted the School Department to oppose the performance. After consulting with district lawyers, former Superintendent of Schools Kristan Rodriguez made the decision to remove the booking, interim Superintendent Bill Ryan said.

“Taking students to a worship service, much less participating in that service as part of a school-sponsored event, is a flagrant violation of the Establishment Clause. Please put a stop to it,” said the letter signed by Richard B. Katskee, legal director of Americans United.

“The Establishment Clause of the First Amendment to the U.S. Constitution prohibits governmental action that communicates an “endorsement of religion,'” the letter said.

A group of former students and their parents have protested the move, writing in a letter to The Sun and the Nashoba Valley Voice that the decision was made without community input.

One of the signers, Lisa McCarron, said she is all for the separation of church and state but that one voice should not trump 40. “The issue is the lack of voice the parents have had,” she said.

After the administration decided not to allow a trip in an earlier year, students and parents met with the School Committee. They got the trip approved as part of a democratic process, McCarron said. “That in itself was a wonderful learning experience.”

The parents and students argue that none of the students objected, complained or felt pressured to perform at the Easter Mass, an honor for which they competed with more than 800 choirs. The complaint did not even come from anyone connected with the trip.

Lathrop confirmed to WBZ-TV she issued the complaint. She did not return several phone calls seeking comment.

Katskee, in a brief phone interview, said the trip’s optional nature did not make a difference.

The choir has a history of distinguished performances — in 2012, the chorus was heard at the summer Olympics in London. It regularly competes in competitions up and down the East Coast.

They have also turned down opportunities to perform for the queen of England and at a presidential inauguration, said Director Timothy Savoy. They also said no to a regular gig each August as the house choir at Canterbury Cathedral — not for religious reasons but because too many singers leave each year for college, Savoy said. “It’s not possible, but it’s a great honor.”

“We’re invited to go on these things because of our level,” Savoy said of the 26-member chorus.

Membership in the chamber chorus is by audition only, and Savoy called it a grueling and very difficult audition that is open only to students who have completed at least a semester of chorus.

The time and dedication of the singers pays off.

The music they perform is the same as that of college-level and professional choirs. Listeners cannot believe that the polished group singing complex music without instrumental accompaniment is made up of 14- to 18-year-olds, Savoy said.

“They’re a very committed group,” he said. “It’s one fourth of their day for a whole year.” The class meets for an hour and a half, five days a week.

The European trips were arranged through KI Concerts, which specializes in performance travel. “They’ve got contacts all over the performance world,” Savoy said.

Even though the basilica performance is off, the chorus will be performing at other venues, Savoy noted.

And the trip for the 26-member ensemble has a cost. The chamber parent group has committed over $96,000 for the group, but another $14,000 is needed to help students who cannot afford the trip.

Fundraising is underway. A benefit concert by Entrain, a Martha’s Vineyard-based six-piece instrumental and vocal group, is scheduled for Jan. 29 at the Devens Common Center at 31 Andrews Parkway in Devens.

The event begins at 6:30 p.m., with a silent auction and reception. The chamber chorus sings at 7:30 p.m. Entrain goes on-stage from 8 p.m. to 10 p.m. for listening and dancing.

Tickets are $40. A $75 ticket gets you premium seating, appetizers, a signed CD and a meet and greet with the band. A dinner menu and cash bar is available.

To order tickets to the event, please email:chambertickets@gmail.com.

For additional information about the chamber chorus, or to make donations for the trip, visit gdchamber.org/home. They can also be found on Facebook.

Including the chorus, more than 80 Groton-Dunstable Regional High School students will go abroad this spring. Plans are made for trips to Argentina, Japan, and England and Scotland.

Follow Anne O’Connor on Twitter and Tout @a1oconnor.