Beijing concertgoers say they were prevented from displaying rainbow-related imagery at a pop singer’s performance on Saturday, in a sign of the increasing squeeze on LGBTQ expression in China.

Fans attending a concert by Taiwanese singer Chang Hui-mei — better known by her stage name A-Mei — say they were prevented from wearing shirts with rainbows on them inside the Cadillac Arena in Beijing, according to participants who posted about the incident on social media.

A person who wrote about the concert on China’s Instagram-style Xiaohongshu service said a security guard at the venue asked thim to turn his shirt inside out, as a rainbow had been drawn on the front. In another post, a person said they were stopped by security because their shirt changed colors based on reflective lighting.