Football fans from around Europe have written to UEFA president Aleksander Ceferin to call for safe standing to be allowed at Champions League and Europa League matches.
Grounds in several European leagues, including Germany's Bundesliga, include safe standing areas but their use is not permitted in the continental club competitions.
Now, adopting the slogan "Europe Wants to Stand," fans' groups from 13 countries including Germany, France, England and Spain are urging Ceferin and UEFA to think again.
An open letter to the UEFA president will be backed by shows of support for safe standing at European games during Borussia Dortmund's Champions League match against Tottenham on Tuesday and Bayern Munich's clash with Liverpool next week.
"Twenty-one years ago, UEFA introduced a ban on standing at international matches," the open letter to Ceferin said.
"In the name of the majority of supporters across the continent, we urge you to reconsider this ban and give us the choice of whether to sit or stand at football matches."
Jan-Henrik Gruszecki, of Borussia Dortmund fans' group Sudtribune Dortmund, said: "There are three main reasons for our protest.
"A vibrant fan culture needs standing terraces. Where there are only seats, fan culture has slowly descended into non-existence.
"Why should something not work in the European cup competitions when it works perfectly in several European top flights? The Bundesliga is a prime example.
"Moreover, it's dangerous for those on the terraces if you have makeshift seats. People will stand anyway, and falling over the seats can result in dangerous injuries. What we at Dortmund have for European games is a de facto standing terrace with seats.
"Lastly, seats are just more expensive than standing. It's different at Dortmund, but not at most stadiums.
"Our arguments, therefore, are culture, safety and pricing."
The open letter said the increasing cost of tickets for Champions League and Europa League matches "has led to the exclusion of young and low-income fans."
It added: "It is our belief that stadia must be open to people from all walks of life, and the provision of tickets in standing areas is one of the easiest ways to achieve this objective."
Information from ESPN FC's Germany correspondent Stephan Uersfeld was used in this report.