The US tightened entry rules for Hungarians under its visa-waiver program, citing security concerns about a fast-track naturalization plan Prime Minister Viktor Orban put in place for people living outside Hungary’s borders.

The US will limit the number of times Hungarians can enter to once a year, rather than allowing multiple visits, and it will cut the period that electronic authorizations are valid under the ESTA program to one year, instead of two now.

“This change will go into effect immediately and remain until the security concerns underlying it are addressed,” the embassy said. The restrictions will only apply to new ESTA approvals and don’t prohibit travel to the US. Hungarians are also allowed to submit regular visa applications.

The US has been a vocal critic of Hungary over its lukewarm support of Ukraine after Russia’s invasion, as well as for the erosion of the rule of law under Orban’s 13-year rule. The new steps over entry into the country, however, are separate to that, according to a senior US government official, who asked not to be identified.

Still, the announcement came a day after Hungary’s ruling party boycotted a parliament meeting on Monday, torpedoing opposition efforts to ratify Sweden’s accession into NATO. Hungary and Turkey are the only members of the alliance yet to approve Sweden’s entry bid, blocking an expansion triggered by Russia’s invasion of Ukraine.

The naturalization program that’s under US scrutiny ran from 2011 to 2020 and granted citizenship to almost 1 million people as Orban pursued a nationalist vision to enfranchise mostly ethnic Hungarians living outside of his country’s borders.

But background checks were inadequate and some people who received passports from the European Union and NATO member were alleged criminals and people using fake identities, raising serious security vulnerabilities, according to the US official. Some had no connection to Hungary, the official added.

Hungarian authorities had refused to address the concerns despite years of bilateral talks with the US, including during the previous administration led by former President Donald Trump.

Hungary’s government said its refusal to share data on its dual citizens had prompted the US restrictions. Some of Hungary’s neighbors bar dual citizenship, putting those living there and also holding Hungarian passports in a potentially precarious position.

“Hungary doesn’t share that with anyone because the safety of Hungarians abroad is at stake,” the Interior Ministry said in a statement, referring to its of passport holders who live abroad.

Currently the citizens of 40 countries have access to the ESTA program, including most of Hungary’s EU allies, which allows people to travel to the US for business or tourism for stays of up to 90 days without a visa.

(Updates with Hungarian government’s reaction in ninth and 10th paragraphs.)