The Palestinian Election Commission has said parliamentary elections scheduled for 17 July will have to be delayed.
Hamas have made strong showings in recent local elections
It says it needs at least two months from the time a new election law is ratified to prepare the vote.
But the new law is being held up in a dispute between Palestinian leader Mahmoud Abbas and parliament.
Parliament has approved a law allowing two-thirds of the MPs to be chosen in districts, and one-third from party lists. Mr Abbas has refused to sign it.
He wants all MPs to be chosen from party lists. Correspondents say he believes this would favour his ruling Fatah party.
The militant group Hamas has made a strong showing in recent local elections, and many observers believe it could seriously challenge Fatah's dominance of the Palestinian parliament.
Mohammed Ghazal, a Hamas spokesman, accused Fatah of trying to manipulate the electoral process.
"We see talk of technical difficulties with the election as an excuse to delay it in their own interests, because they expect Hamas will win," he said.
In a statement the commission said it could carry out the election on time in line with the old election law. It called on Mr Abbas to issue a presidential decree with a new election date as soon as possible.