Pakistan’s main anti-corruption watchdog has summoned former premier Nawaz Sharif and his sons Hussain and Hasan to appear before investigators in Lahore on Friday in connection with graft allegations linked to a steel mill once owned by the Sharif family.The National Accountability Bureau (NAB) also summoned Sharif’s close aide, finance minister Ishaq Dar, on August 23 in light of the Supreme Court’s orders that sent the former premier packing last month, local media reported.On July 28, the Supreme Court had disqualified Sharif for being dishonest while declaring his assets. The top court also asked the NAB to file cases within six weeks against Sharif, his sons, son-in-law Captain (retired) Muhammad Safdar and Dar for alleged money laundering and corruption.The court’s ruling was issued in the case related to the Sharif family’s offshore assets that were revealed in the Panama Papers leaks. Most of the cases referred to the NAB by the Supreme Court are related to steel and sugar mills started by the Sharif family and several offshore firms.NAB officials were quoted by the media as saying that Sharif and his sons would be quizzed about the Al-Azizia Steel Mills case. The mill was started by the Sharif family but later sold to another businessman. An unnamed NAB official told the Dawn newspaper that this would be “the first of many cases” that the agency would probe.The NAB has also sought assistance from foreign countries to probe cases against the Sharif family, Geo News channel reported. Sharif has not yet decided whether he will appear for questioning by the NAB. “Nawaz Sharif is considering boycotting the NAB proceedings because he thinks it is very much likely that, like the Panama Papers case, he may not get justice in its case as well,” a senior PML-N leader told PTI.The cases being taken up by the NAB could have serious implications for Sharif, especially since Pakistan is set to go to the polls next year. His PML-N party remains the strongest political force in the country but any adverse outcomes in these cases could affect the party’s prospects.Sharif has repeatedly questioned the Supreme Court’s decision to disqualify him for not declaring a salary that was due to him from his son’s Dubai-based firm, Capital FZE. Sharif has said he never received any money from the company.Seeking a stay against his disqualification, Sharif on Tuesday filed a review petition against the July 28 verdict of the Supreme Court. He challenged the court’s judgment, saying the final order contained errors and was liable to be reviewed.In a related development, Sharif’s arch-rival, Pakistan People’s Party leader Asif Ali Zardari, will also face anti-corruption proceedings as the NAB has expedited the last pending case against him. In the wake of the recent judgement against Sharif, an anti-corruption court, with the consent of the NAB, has initiated daily hearings in the case against Zardari that is related to the assets in Pakistan and abroad that he allegedly acquired through illegal means. The case was filed in 2001 and closed six years later under an amnesty granted by the regime of former military ruler Pervez Musharraf.