Frank Oz leveled charges at a Sundance Film Festival event called “Hero,” saying it duplicated an important element of the Off Broadway show he directed, “In & Of Itself.”

Director and “Muppets” voice actor Oz began posting comments on Twitter Saturday, noting that Sundance’s multi-sensory virtual reality event was “ripping off” an element of “In & Of Itself,” a one-man show starring performance artist and illusionist Derek DelGaudio, which has been running in New York since April 2017.

Audience members entering the theater for “In & Of Itself” are asked to choose a perforated card from a wall. Each card reads “I AM” above the perforation; the lower half of each card is unique and includes any number of descriptive identifiers, from “publisher” to “bad mamajama” to “witness.”

Those cards are at the center of the dispute; based on images posted on DelGaudio’s Twitter feed Sunday, “Hero” featured a similar wall of cards, divided into “I AM” and a collection of personal identifications like “mentor,” “father,” “son.”

As DelGaudio noted in his tweet, “It’s simple. Shitty, but simple…. People saw my show, appropriated the relational aesthetics, and set up shop at @Sundancefest.”

“Hero” is a virtual reality collaboration created by creative agency Inhance Digital and collaborator Ink Stories, exploring “human resilience in time of crisis,” according to a press release. The experience ran Jan. 18-28 at the Kimball Art Center.

On Monday, Ink Stories co-founder Navid Khonsari posted a letter on Twitter addressed to DelGaudio and Oz, apologizing for the “unfortunate misunderstanding” while also justifying the use of “I AM” cards by saying they draw “inspiration from more than sixty years of social impact work.”

He added that he would be “modifying our use of ‘I AM’ for our future iterations.”

Other celebrities posted messages of support on Twitter for DelGaudio’s show, including Patton Oswalt, Adam Savage, and “Wait! Wait! Don’t Tell Me” host Peter Sagal. “Itself” producer Neil Patrick Harris retweeted Sagal’s comment, but has not issued a statement of his own.

“This all came as a big surprise when people on Twitter pointed out what was going on,” DelGaudio told Variety in a statement. “As of now, we are working to resolve it and look forward to putting the mess behind us.”

Oz declined to comment; Harris and Khonsari did not respond to requests for comment at press time.