The board in question is the one chaired by Pipat Yingseree and including GPO managing director Suvaj Siasiriwattana.
Vachira Bothapiboon of the Rural Doctors Society, who represents the eight networks, submitted evidence to the DSI.
It involves the construction of the GPO's drug factory in Rangsit of which contract was scrapped by Mr Pipat and the GPO board.
They later drafted new terms of reference which favoured a company which had abandoned a GPO job earlier.
They failed to blacklist the company against the recommendation of the Audit General's Office.
"By now, it's clear the factory cannot open by schedule, causing damage to the GPO," said Dr Vachira.
"This means warranty of machinery and equipment already imported or bought will expire soon, which is a shame because it has not been used. For instance, the warranty of chillers worth hundreds of millions of baht ended last month," he said.
Meanwhile, the GPO factory on Rama VI Road will have to be shut down in October for an upgrade to meet Good Manufacturing Practices standards, he said.
The Rangsit factory's construction delay will affect medicine production, triggering shortages of some medicines.
"After the board voted to remove GPO managing director Witit Artavatkun for alleged corruption in the construction of a vaccine factory, no progress has been made on the factory. A Japanese vaccine company has pulled back its aid amid conflicts between the board and Dr Suvaj," Dr Vachira said.
Nimit Thien-udom, director of the Aids Access Foundation, said he would submit a letter to the National Council for Peace and Order for the removal of Narong Sahamethapat, permanent secretary of the Public Health Ministry, and Dr Suvaj.
He said there was clear evidence Dr Suvaj had cut back on the production of some popular low-margin drugs, a move not in the best interest of the public.
He urged the appointment of a new board based on merits and without conflicts of interest.