The National Accountability Bureau (NAB) has summoned Opposition Leader in Punjab Assembly Hamza Shahbaz in Ramzan Sugar Mills case on Monday (today).The Pakistan Muslim League-Nawaz (PML-N) leader has been summoned as chief executive of the mills. Earlier this week, an accountability court in Lahore had indicted Opposition Leader in National Assembly Shahbaz Sharif and his son Hamza in the Ramzan Sugar Mills reference. The father-son due is currently on bail in the reference. Both were awarded bails by the Lahore High Court (LHC). The NAB has filed a reference accusing former Punjab chief minister Shahbaz Sharif, his son Hamza Shahbaz and others for causing losses to the national exchequer and misusing authority by sanctioning construction of a bridge to facilitate the sugar mills.NAB officials say Shahbaz Sharif, being chief minister of Punjab, misused his authority by issuing directives for the construction of a 10-kilometre-long drain in Chiniot primarily to benefit the sugar mills owned by his sons. Shahbaz and Hamza have been accused of fraudulently causing a Rs 213 million loss to the national exchequer.