Tens of thousands in Budapest have protested against Hungary's new constitution, which they believe will weaken democratic institutions.

The protest took place near the State Opera House Monday as the center-right Fidesz government led by Prime Minister Viktor Orban celebrated the new “Basic Law” with a gala. The protestors chanted anti-Orban slogans as government dignitaries arrived at the gala. But Mr. Orban says the new constitution completes the country's transition from communism to democracy.

The Fidesz party won a two-thirds majority in 2010 elections and has rewritten a large portion of the law. Critics fear the new constitution, which went into effect on January 1, curbs constitutional court powers, threatens the media and ends judicial independence.

The European Union, the United States and international watchdogs groups such as Amnesty International have voiced strong opposition to the law, which changes the country's name from “the Republic of Hungary” to simply “Hungary.”

Hungary is facing possible recession in 2012, but the current dispute has cast doubt over talks with the European Union and International Monetary Fund to reach a critically needed new financing agreement.