Some opponents of the changes staged a protest at Fidesz party headquarters last week.
He served as an MEP for the ruling right-wing Fidesz party before being appointed president in the summer of 2010.
Hungary's parliament has adopted a package of constitutional changes proposed by the ruling Fidesz party which critics say undermine democracy.
Mr Orban has been able to push through changes because of the two-thirds majority his Fidesz party and its allies enjoy in parliament, following the 2010 election.
In the 2010 election, a conservative coalition consisting of Mr Orban's Fidesz party and the Christian Democratic People's Party won two-thirds of the seats in parliament, and this powerful majority has made it possible for the governing parties to push through several pieces of controversial legislation.
During his first government, between 1998 and 2002, Orban's Fidesz party designated an annual Holocaust memorial day and after returning to power in 2010 banned uniformed groups like the Jobbik-affiliated Hungarian Guard, whose marches in Budapest and countryside villages were meant to intimidate Jews and Hungary's large Roma minority.
His party, Fidesz, insists that the constitutional changes conform with Hungary's legal responsibilities as an EU member.
The leader of Fidesz, Hungary's centre-right party, won a stunning two-thirds majority in parliament on April 25th, taking 263 of the 386 seats.
Fidesz's electoral list included a second party, the Hungarian Democratic Forum.
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