By Krisztina Than and Marton Dunai
BUDAPEST (Reuters) - Hungary's ruling Fidesz party signalled on Monday it could push on with legislation to crack down on organisations promoting migrant rights as soon as parliament reconvenes after Prime Minister Viktor Orban's sweeping election victory.
The right-wing nationalist projected himself as a saviour of Hungary's Christian culture against Muslim migration into Europe, an image which resonated with more than 2.5 million voters, especially in rural areas.
His Fidesz party won a two-thirds majority for the third time straight time in Sunday's election, meaning he again has the powers to change constitutional laws - potentially paving the way for further friction with the European Union.
The victory could embolden Orban to put more muscle into a Central European alliance against EU migration policies, working with other right-wing nationalists in Poland and Austria, and further expose cracks in the 28-nation bloc.
A Fidesz spokesman told state radio on Monday: "After parliament is formed, at the end of April ... in early May in the next parliament session we can start work ... that is needed in the interest of the country, which could be the Stop Soros legal package."
The proposed legislation is part of Orban's campaign targeting Hungarian-born U.S. financier George Soros, whose philanthropy aims to bolster liberal and open-border values.
According to the bill submitted to parliament before the election, it would impose a 25 percent tax on foreign donations to NGOs that the government says back migration in Hungary.
Their activity would have to be approved by the interior minister, who could deny permission if he saw a "national security risk".
Last month, Orban told state radio the government had drafted the bill because activists were being paid by Soros to "transform Hungary into an immigrant country". Soros has rejected the campaign against him as "distortions and lies".
Analysts at Hungarian think tank Political Capital said Orban's election landslide reflected the success of his efforts to consolidate power around Fidesz, which controls state media and regional newspapers via business allies.
"Hungary has become a successful laboratory of illiberal governance with an institutional system tailor-made to serve Fidesz's purposes and goals," it said.
Indeed, the Organisation for Security and Co-operation in Europe watchdog said parties could not compete on an equal basis in the election, which was held in an adverse climate as freedom of the media and association were restricted.
"Voters had a wide range of political options, but intimidating and xenophobic rhetoric, media bias and opaque campaign financing constricted the space for genuine political debate," the OSCE, which monitored the vote, said. It said the technical administration of the election had been transparent.
A spokesman said European Commission President Jean-Claude Juncker would write to Orban to congratulate him on his victory and emphasise that defending democracy and values was the common duty of all member states with no exception.
European Council President Donald Tusk said in a statement: "During your renewed term as prime minister I count on you to play a constructive role in maintaining our unity in the EU."
German Chancellor Angela Merkel congratulated Orban, a German government spokesman said, adding she would work with his new government despite differences on migration.
French far-right leader Marine Le Pen was the first to congratulate Orban. Poland's deputy foreign minister and envoy to the EU, Konrad Szymanski, hailed his victory as "a confirmation of Central Europe's emancipation policy".
Before the election, Hungary had already signalled it would be looking to expand co-operation on migrant policy with neighbouring Austria, the only country in Western Europe with a far-right group in government, as well as Italy, where the centre-left Democratic Party lost to anti-establishment and right-wing parties that campaigned hard against immigration.
"Orban is implementing sustainable and correct policies for the people of his country ... Hungary's voters have rewarded that once again," Austrian Vice Chancellor Heinz-Christian Strache, leader of the far-right Freedom Party, said.
According to preliminary results with 99 percent of votes counted, National Election Office data showed Fidesz winning 134 seats, a two-thirds majority in the 199-seat parliament. Nationalist Jobbik won 25, while the Socialists were projected in third with 20 lawmakers, among the remaining seats.
The final result is expected later this month.
Orban, Hungary's longest-serving post-communist premier, opposes deeper integration of the EU and - teaming up with Poland - has been a fierce critique of Brussels' policies.
Since coming to power in 2010, his government has locked horns with the European Commission over reforms that critics say have eroded democratic checks and balances and weakened the independence of the media.
Some of the NGOs that could be hit by the new law said they expected a hardening in the new government's stance.
"With a two-thirds majority, there can be no doubt they can and will do it," Hungarian Civil Liberties Union director Stefania Kapronczay said. "This is terrifyingly serious."
(Writing by Krisztina Than and Gergely Szakacs; additional reporting by Francois Murphy in Vienna, and Robert-Jan Bartunek and Julia Fioretti in Brussels; Editing by Alison Williams)