Lawyers for former Prime Minister Nawaz Sharif filed a petition in the Supreme Court Tuesday challenging his expulsion to Saudi Arabia, setting up another confrontation between the judiciary and Pakistan's military ruler as he battles to hold onto power.

President Gen. Pervez Musharraf sent Sharif, the premier he ousted in a 1999 coup, back into exile on Monday hours after the opposition leader landed on a flight from London. Sharif, who had intended to return home to lead a campaign against Musharraf, was also charged with corruption during his four-hour stay in the country.

Sharif's lawyers on Monday petitioned the Supreme Court to start proceedings against the government for contempt in relation to the deportation. Last month, the court ruled that Sharif had an inalienable right to return home.

"We will fight this battle in the court of law," Sharif's nephew, Hamza Sharif, told reporters on the steps of the Supreme Court after the petition was filed. "We are fully confident that we will win, God willing."

The Supreme Court has emerged as a check on Musharraf's dominance since his failed attempt to sack the country's top judge earlier this year that sparked a nationwide protest movement.

It is already hearing petitions challenging Musharraf's holding of the post of army chief and president simultaneously and his eligibility to contest upcoming presidential elections. It is also pressing the government to provide information about the fate of hundreds of people allegedly held by Pakistan's shadowy intelligence agencies on accusations of terrorism and anti-government activities.

Analysts say Monday's decision to expel Sharif will deepen Musharraf's unpopularity in Pakistan and reinforce impressions that he is an authoritarian leader. It also could undermine the legitimacy of legislative elections due by January 2008.

Ali Ahmed Kurd, a senior member of the Pakistan Bar Council, said lawyers across the country were boycotting court proceedings to protest Sharif's deportation.

"The government intentionally and willfully violated the Aug. 23 ruling of the Supreme Court," he said. "The government wants to curb the independence of the court that it achieved through the lawyers' movement ... We should back the independence of the judiciary."

Deputy Information Minister Tariq Azim told the British Broadcasting Corp. on Monday that Musharraf's government obeyed the Supreme Court ruling to let Sharif enter the country, but that the former premier chose to go back into exile to avoid facing trial.

Sharif was originally exiled in 2000 following the coup. Accused of denying landing rights to a plane carrying Musharraf that was short on fuel, Sharif was jailed but later released and sent to Saudi Arabia after allegedly pledging not to return for a decade.

"It was a choice given to him that either he goes to a detention center and be detained and tried, or he goes and completes his 10-year (exile) agreement that he has signed with the Saudi government," Azim told the BBC.

"No hindrance or obstacle was placed upon his entry into Pakistan," Azim said.

Sadiq ul-Farooq of Sharif's Pakistan Muslim League-N party called the government's claim that Sharif chose to go back into exile a "baseless concoction" and that he had volunteered to be arrested by police at Islamabad airport after he was served a warrant.

"He (Sharif) said, 'If you have any cases against me, arrest me and send me to jail.' He offered his wrists to them," ul-Farooq said.

He estimated that more than 5,000 Sharif party workers and leaders have been arrested nationwide in recent days, including the party's chairman and former Pakistan President Rafiq Tarar. Authorities have confirmed that hundreds were rounded up ahead of Sharif's return.

His deportation also drew immediate criticism from the European Union, which noting the Supreme Court ruling denying authorities the right to block the return of Sharif, who was twice elected prime minister in the 1990s.

State Department spokesman Sean McCormack said the deportation "runs contrary to the Supreme Court decision," but would not comment further because the matter was "still under legal consideration."