The high court had on Tuesday restrained the Punjab government from implementing a notification about fixing the ex-mill and retail price of sugar at Rs 80 and Rs 85
The FIA Lahore office has started summoning the representatives of sugar mills' administrations from March 31.
The sugarcane commissioner has conveyed to Prime Minister Imran Khan regarding a shortfall in the stocks by 300,000 tonnes.
The government would be able to save Rs836 billion from the agreements with the IPPs after they get a final nod from the federal cabinet.
According to FBR officials, a session of sugar mills and vendors will be held in Islamabad this week.
"The 'off the book' purchases will harm the provincial government financially", the sources added.
The mills had sought the court's restraining order against the FBR proceedings and declaring the notices dated October 16, 22 and 29 as void.
Millers who delay the payments to cane growers by 15 days will have to pay 11pc on the overall payment as a markup as to protect and compensate farmers.
Court rules FIA has powers to carry out the inquiries
The PMSA was working as a frontrunner for sugar mafias, the Competitive Commission of Pakistan (CCP) found during the probe.