Citing the Constitution, leaders of the parliamentary opposition to Mr. Karzai said they would stop recognizing his authority after May 22. They called on the United Nations and Western governments to help them appoint a temporary president after Mr. Karzai’s term formally expires.

Image President Hamid Karzai, shown in a Kabul shop, has announced that he will seek re-election this year. Credit... Lynsey Addario for The New York Times

“After May 22, Karzai’s continuation will not be legitimate for either us or the Afghan people,” said Aqa Fazil Sancharki, a spokesman for the United Front, whose members control about a third of the 241 seats in the lower house of Parliament.

A spokesman for Mr. Karzai said he would respect the commission’s decision to delay the vote. Mr. Karzai, who was elected to a five-year term in 2004, has led the country since the ouster of the Taliban in November 2001. He has declared his intention to seek re-election, and while a number of prominent Afghans have said they may also run, only three lesser-known candidates have declared so far.

The election this year will come at an especially difficult time, with the Taliban insurgency challenging the government’s writ in many areas.

A United Nations spokesman said the organization had resigned itself to the delay, given that there did not appear to be enough time to have everything in place by late May. “At this point, it has become a pragmatic necessity,” said Adrian Edwards, a United Nations spokesman in Kabul.