Labor Shadow Communications Minister Michelle Rowland and Shadow Finance Minister Jim Chalmers referred to Switkowski's quote, "I could certainly generate - and do generate - figures around $50 billion for the value of this company in the early 2020s.”
They described it as a "concerning departure from reality".
During his statements to Estimates, Switkowski also ruled out a write-down of the NBN, though he said this was a personal view.
Rowland and Chalmers said Switkowski's estimate was at odds with the analysis of accounting firm Price Waterhouse Coopers who had estimated that the network was worth $27 billion in 2016.
The Labor duo also cited the assessment of ratings agency Standard and Poor's who said in July a write-down of the NBN appeared inevitable.
S&P also said the NBN would not return a profit from the billions invested in the project, adding that the NBN Co's business model had led to telcos investing heavily in mobile services to avoid paying the company's inflated prices.
"Given the significant difference of opinion, Labor calls on the NBN Co Chairman to provide evidence or analysis to support his claim," Rowland and Chalmers said.
"If he cannot, he should withdraw or correct the statement. As it stands, the Liberals’ multi-technology mix is $22 billion over budget and four years behind schedule.
"No amount of wishful thinking can undo this fact."