LISBON—Portugal's president sent the 2013 budget to the country's highest court for review, an unusual move that highlights deepening opposition to a two-year austerity drive.

President Aníbal Cavaco Silva, who is the head of state and like Prime Minister Pedro Passos Coelho belongs to the right-of-center Social Democratic Party, signed the budget bill into law on Monday, but expressed reservations the next day. In a televised address to the nation late Tuesday, he expressed doubts about the budget's "distribution of...