Pro-Europe activists could take over the Last Night of the Proms by waving EU flags at London's Royal Albert Hall on Saturday.
A social media campaign has been taking place to show "solidarity" with the EU at the event, which comes almost three months after the pro-Brexit referendum vote.
Brexiteers described the campaigners as "sore losers".
The campaign was launched on a Facebook group, which has now been closed, but money is still being raised for the flags on Crowdfunder, with more than £1,100 raised by Thursday morning.
Organisers hope to raise enough money for 5,000 flags.
"As music is such an international activity that benefits greatly from our membership of the EU this event feels an appropriate venue to show UK solidarity with the EU," a message on the page said.
"The event is televised and has a very high profile. Concert goers waving EU flags along with the Union Jack would send a message to the world and our own people about how much music lovers value the EU."
It remains to be seen what will happen on the night, but the campaign has been dismissed by pro-Brexit campaigners.
A spokesman for the Leave.EU campaign told Breitbart London: “It’s been over two months since the vote, they need to stop being sore losers and get over it. Their constant attempts to undermine democracy are sad and getting very boring”.