Anna Patalong wore a yellow ball gown with a blue waistband and a necklace covered in gold stars as she performed in Classical Spectacular show on Sunday.
A concert goer took to Twitter to say she was disconcerted by Patalong's choice of dress, despite being a Remainer herself.
"In my opinion the public paid to come to a classical music concert and not a political rally. As much as I applaud your wife for having the guts to quite literally nail her colours to the mast, I feel it was inappropriate to do it at a concert," Angela Whelan wrote, addressing Patalong's husband, baritone singer Benedict Nelson, on Twitter.
Some agreed with Whelan and suggested that "classical music is and has always been apolitical," while others accused the artist of turning the performance into a "PR stunt."
In contract, some commentators mocked the incident with photos and memes.
According to the concert's producer, the complaint by the member of the audience had not influenced the company's request for Patalong not to wear the dress again. However, the singer's husband insisted the reason for the request was the "provocative" nature of the dress.
Classical Spectacular has been playing for around 3 decades, featuring classical music and multicoloured laser displays in the March 2019 season.