An Argentine prosecutors' office said on Tuesday that it found irregularities in a planned auction to provide maintenance to the Paraguay-Parana river, a key route for grains transport.
The tender, which had been announced in November, was set to go live on Wednesday.
Prosecutors found evidence of, "serious and evident irregularities in the wording of the tender documents," they said in a report detailing their findings.
The auction would have assigned contracts for dredging and buoying Argentina's stretch of the Paraguay-Parana waterway, a key transport route to the sea from inland areas of Paraguay, Bolivia and southern Brazil.
Argentina uses the 3,400 km-long (2,100 mile-long) waterway to move nearly 80 per cent its foreign trade, including its massive farm exports such as processed soybeans, corn and wheat.
Some foreign dredging firms had already decried the auction guidelines, arguing they favored the waterway's current operator, Belgian firm Jan de Nul. Opposition lawmakers requested an investigation into the process.
(Reporting by Maximilian Heath and Walter Bianchi; Editing by Anthony Esposito and Sarah Morland)