EU foreign policy chief Catherine Ashton and Neighborhood Policy Commissioner Stefan Fule expressed concern that a Ukrainian court upheld a verdict against Interior Minister Yuriy Lutsenko.
Lutsenko is serving a four-year prison term on charges of embezzlement. He was interior minister under former Prime Minister Yulia Tymoshenko, who's serving a seven-year prison term after being convicted on charges of abusing her authority in 2009 deal with Russian energy company Gazprom.
Lutsenko's family said he's in poor health.
Ashton and Fule said they've expressed their "strong concern" about the legal standards in Ukraine.
"We call on the Ukrainian authorities to step up cooperation with the mission to redress the effects and remove the concerns regarding selective justice," they said.
The European Parliament passed a resolution in March that expressed concern for the general lack of commitment to democracy and impartial justice in Ukraine.
It said it would consider signing an association and trade deal with Ukraine during a late 2013 conference planned in Lithuania if the government takes its concerns seriously.