Inna Shevchenko, 21, an activist in the Femen group, peeled off her top, revealing the words "Fuck Euro 2012" on her torso, and grabbed hold of the 60 cm (two feet) high cup while it was being exhibited in a central square in Dnipropetrovsk, according to a video clip released by Femen.
As security guards moved in on her, another activist, standing next to the cup ostensibly waiting to be photographed by sightseers, stripped off to the waist to display the same slogan.
Femen organisers said the second activist was a 46-year-old French journalist from a French women's magazine. "She also supports our struggle against sexism and prostitution and decided to take part," said Femen spokeswoman Anna Hutsol.
Both women were detained by police.
The Kiev-based Femen is focusing its topless protests for women's rights on next month's tournament, which Ukraine is co-hosting with Poland.
Femen says Euro 2012, which will run in Ukraine from June 9 to July 1, will lead to a surge in prostitution in the former Soviet republic and entrench the country as a sex tourist destination in Europe.
It is threatening to carry out a blitz of stunts against the tournament.
Another Femen activist staged a similar protest in Kiev earlier this month, seizing hold of the same cup while it was on public display in the capital.
The 8 kg (17 lbs) Henri Delaunay cup is on a tour of Ukraine so Ukrainians can have souvenir photographs taken of themselves alongside it.
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