(CNN) -- SeaWorld's "Bands, BBQ and Brew" concert series may be down to just food and beer soon as Trisha Yearwood joins the list of artists canceling shows.
Willie Nelson, Heart, Barenaked Ladies and Cheap Trick previously withdrew amid pressure from fans who signed online petitions, tweeted and posted on Facebook pages demanding they not play at the Orlando theme park.
Fans became upset after watching the CNN documentary "Blackfish," which first aired on CNN in October. The film tells the story of the killing in 2010 of a SeaWorld trainer by an orca. It raises questions about the safety and humaneness of keeping killer whales in captivity.
"In light of recent concerns, Trisha has decided to remove the February 22 date from her upcoming tour plans," the country singer's representative told CNN Thursday. The news quickly lit up Twitter.
"We expect that other artists will be targeted in this campaign," SeaWorld spokesman Nick Gollattscheck told CNN after Cheap Trick canceled Wednesday.
The park's concert schedule -- which also previously listed REO Speedwagon, Martina McBride, 38 Special, Justin Moore and Scotty McCreery -- has disappeared from SeaWorld's website. It now simply promises "incredible concerts with top artists in classic rock and country music."
SeaWorld is working to book replacement acts, Gollattscheck said. "We'll announce the full lineup of bands when all artists have been confirmed. We'll repost the schedule on our site then."
The Canadian rock band Barenaked Ladies was the first to cancel, reacting to a petition posted on Change.org.
"This is a complicated issue, and we don't claim to understand all of it, but we don't feel comfortable proceeding with the gig at this time," the band said on its Facebook page.
Sisters Nancy and Ann Wilson of Heart did not elaborate last week when they announced their decision to cancel at SeaWorld, although they acknowledged it was "due to the controversial documentary film."
"While we're disappointed a small group of misinformed individuals was able to deny fans what would have been great concerts at SeaWorld," Gollattscheck said.
SeaWorld said it would like the musical artists to learn for themselves about SeaWorld.
"The bands and artists have a standing invitation to visit any of our parks to see firsthand or to speak to any of our animal experts to learn for themselves how we care for animals and how little truth there is to the allegations made by animal extremist groups opposed to the zoological display of marine mammals," Gollattscheck said.
SeaWorld says the documentary ignores the park's conservation efforts and research.
CNN's Jane Caffrey and Carolyn Sung contributed to this report.