The changes were agreed at the height of the "Orange Revolution" as part of a deal to win broad agreement on re-staging a rigged presidential election. Yushchenko won the rerun and took office in January.
But during a live television interview today, Yushchenko said the changes now threaten political stability and efficiency. He said the issue of a referendum will be on his agenda, but did not say when.
Under the changes due to go in effect on 1 January, the president is no longer free to nominate the prime minister and other key ministers.
Yushchenko has been increasingly critical of the new arrangements as parliament lacks a stable majority and he has had trouble pushing key reforms through the assembly.
Parliamentary elections are set for March.