"The death penalty is not compatible with European values," Steffan de Rynck, the European Commission spokesman, said.
Lech Kaczynski - whose identical twin brother is Poland’s prime minister - said last week that the EU would come to see that the death penalty is justified for murder.
"Countries who give up this penalty award an unimaginable advantage to the criminal over his victim, the advantage of life over death," he told a radio station on Friday.
Poland officially abolished capital punishment in 1997 but the practice had been halted soon after the fall of communism in 1988.
Abolishing the death penalty is a pre-condition for starting membership negotiations with the 25-nation bloc.
Kaczynski's conservative Law and Justice (PiS) party won power last year promising a tough stance against corruption and crime.
The League of Polish Families (LPR), a minority party in Poland's governing coalition, has announced a Europe-wide campaign to restore the death penalty.
"We want to collect half-a-million signatures of European Union citizens on a petition demanding the death penalty for paedophile murderers," LPR vice-president Wojciech Wierzejski said.