US retail giant Costco has apologised after copies of the Bible labelled as “fiction” were found on sale at one of its stores, triggering protests by Christian groups.

Caleb Kaltenbach, a pastor at the Discovery Church in Simi Valley, California, tweeted a picture of the Holy Bible, with a bar-code price sticker clearly labelled “Fiction” last Friday.

“Costco has Bibles for sale under the genre of FICTION. Hmmmm …. ” he wrote, prompting a surge of retweets and comments from both critics and some suggesting the description was accurate.

“DOES Costco sell The Koran under the genre of “FICTION” I WONDER ???” wrote Holly Bishop (@Southerngal1963) on the microblogging site.

But Steven (@SrDurham) asked: “is it not fiction? I think Costco has this correct, please provide factual data to support otherwise.”

Costco sought to downplay the flap, apologising, but saying it was simply an error by a distributor.

“Costco’s distributor mislabelled a small percentage of the Bibles, however we take responsibility and should have caught the mistake,” it said in a statement on Wednesday.

“We are correcting this with them for future distribution. In addition, we are immediately relabelling all mislabelled Bibles. We greatly apologise for this error.”

But it was unclear if that will be enough for local Christians.

“I was completely offended,” Shellie Dungan, a member of Kaltenbach’s congregation, told KTLA-TV, adding: “It’s wrong, and I believe that the Bible is real.”