The presidential election will take place next year, on a date still to be determined.

The governing party had already confirmed that Mr. Maduro will run again, but the opposition has not named any candidates yet.

Now, they may not be able to. The decree could prevent all their candidates from taking part in the election.

The decree, in part, says, “Political organizations, in order to participate in the national, regional or municipal electoral processes, must have participated in the elections of the constitutional period of national, regional or municipal level immediately previous.” Leaders of opposition parties like Henrique Capriles, a former presidential candidate, or Leopoldo López, a political prisoner, have only one option: to try to renew the legal status of their parties by applying to the National Electoral Council, which has been accused of allowing fraudulent practices in previous elections.

On its Twitter account, the United States Embassy in Venezuela offered a rebuke of the decision, saying: “The Venezuelan government and its illegitimate National Constituent Assembly are creating rules as they go. This is not democracy. The different political views make strong democracies.”

Luis Florido, who has been taking part in discussions between the government and the opposition, said the new rule was perplexing. It affects parties that are now in negotiations with Mr. Maduro’s government, he said.