Gadkari's reported decision to rely on the arbitration route to decide on the fate of such projects may cost the exchequer.
Singh said that he had written a letter to the minister "sometime back" but refused to go into its contents.
"I cannot discuss it with you," he said.
When contacted, Road Secretary Vijay Chibber also declined to comment.
In a meeting last month presided over by Gadkari, a decision was taken to clear stalled highway projects through arbitration allegedly bypassing the NHAI chairman.
The Minister is believed to be of the opinion that there was a pressing need to fast track decision-making in the infrastructure sector as delay in projects' execution causes financial losses.
Meanwhile, Planning Minister Rao Inderjit Singh today informed Parliament that as many as 295 infrastructure sector projects worth Rs 150 crore or more are delayed with total cost overrun of Rs 1,01,436 crore.
Out of 720 central sector infrastructure sector projects costing Rs 150 crore and above, 295 projects were delayed, the 346 Flash Report of August 2014 released by the Ministry of Statistics.
The original cost of the 295 delayed projects is Rs 5,48,838 crore and anticipated cost is Rs 6,50,274 crore, thus leading to a total cost overrun of Rs 1,01,436 crore.

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