In a communication to the Ministry of Transport recently, the delta province said this "is in line with the actual situation" but did not say what caused the rethink.
In July it had agreed that the expressway developer, Deo Ca Group of HCMC, would carry out the work through a public-private partnership.
The widening had then been estimated to cost VND9.5 trillion (US$388.3 million) to be shared equally by the government and Deo Ca.
The 51-kilometer expressway links up with the HCMC – Trung Luong Expressway to form the only high-speed highway between the city and the country's agricultural hub, the delta.
It opened to traffic in April this year after being under construction for 13 years, and reduces the travel time between HCMC and Tien Giang from three hours to one hour and 45 minutes.
Costing VND12 trillion (US$494 million), the Trung Luong – My Thuan Expressway has four lanes and no emergency lane.
The second phase will widen it to six lanes plus two emergency lanes.