Budapest is the last country not to approve the Scandinavian country's bid to join the military alliance, following Turkey's approval in January.
Hungary, which has maintained close ties with Russia since its invasion of Ukraine in February 2022, has been dragging its feet for months, even though it says it supports Sweden's proposal in principle.
Agnes Vadai, a member of the country's largest opposition party, told AFP that Prime Minister Viktor Orban was delaying the vote out of "personal arrogance".
Vadai said Orban wanted to "make headlines in the international press while making a gesture to Russian President Vladimir Putin by undermining the unity of NATO and the EU."
THE US INCREASED PRESSURE
For its part, the US has increased pressure on Hungary to approve Stockholm's proposal. In a statement on Friday, the US Embassy reminded Orban that he had promised to act "at the earliest opportunity" and said that "today's session presents him with an opportunity".
The co-chairs of the US Senate's NATO Observer Group also warned that "both time and patience are running out."
For his part, Orban invited his Swedish counterpart to Hungary and expressed the need to "build strong mutual trust" through "more intensive political dialogue".
Swedish Prime Minister Ulf Kristersson accepted the invitation but rejected the idea of "negotiations" and "demands".