MANILA — Two former senators, who voted to evict two large U.S. military bases from the Philippines in 1991, asked the Supreme Court on Monday to declare unconstitutional a new defense pact clinched with Washington, the first legal challenge to the pact.

The case will draw new attention to President Benigno Aquino's battles with the courts, which have blocked many of his administration's reforms since he came to power in 2010, including a landmark law creating a truth commission to examine the wrongdoings of past administrations.

Manila and Washington last month signed a new Enhanced Defence Cooperation Agreement (EDCA) to allow U.S. forces wider access to local bases and construct facilities to store logistics for maritime security and disaster operations.

On Monday, Rene Saguisag and Wigberto Tanada filed a 63-page petition alleging that the government had failed to uphold and protect the country's sovereignty and national interests.

"The executive has circumvented the correct and brave stand by the Philippine Senate in 1991 in refusing to renew the bases treaty by illegally entering into the EDCA," the petitioners said in their submission.

Saguisag and Tanada were among a dozen senators who voted to terminate the military bases agreement signed in 1947 with the United States, a year after the Philippines won its independence from its former colonial masters.

"This will effectively allow them to establish and operate de facto military bases anywhere on Philippine soil, minus the cost of paying for one," the submission said.

Aquino has clashed repeatedly with the Supreme Court and the chief justice was removed in 2012 after an impeachment hearing clearly backed by the president's administration. But, the court has kept its independence, not always voting in his favor.

Public opinion has always been favorable to the United States, particularly in recent times as Manila has become embroiled in disputes with China over Beijing's claim to most of the South China Sea.

Also signing the petition were nationalist and left-wing activists and the son of former Senate president Jovito Salonga, who opposed the presence of U.S. military bases. Many of the signatories turned up at the court house.

Peter Paul Galvez, a spokesman for the defense department, said the new pact in no way violated the 1987 constitution. But he said the petitioners were entitled to voice their opinion.

"We maintain that it's within the constitution and existing laws," Galvez told reporters at the main army base in Manila. "The interest of the country has been paramount in this negotiation."

The military said the accord could upgrade the country's ability to deal with external threats, including against intrusions into its vast maritime borders.