The delayed Aberdeen bypass could cost its builders “hundreds of millions” of pounds more than the contract signed with the Scottish government, it has been claimed.
The £745m 28-mile (45km) bypass was approved by Scottish ministers in 2009.
There have been issues with bridge construction, leading to delays.
North East Labour MSP Lewis Macdonald said the gap between what the government is paying and what it is costing to build is a nine-figure sum.
Transport Secretary Michael Matheson earlier said he held a “constructive” meeting with Aberdeen Roads Ltd on Thursday.
He reported efforts were ongoing to secure a contract variation necessary to open the next section of the project between Craibstone and Stonehaven and Charleston.
The Rural Economy and Connectivity Committee has written to Aberdeen Roads Ltd asking the contractors to give evidence.
Mr Macdonald told BBC Scotland: “I think there’s a lot at stake.
“All the reports we’ve had from the contractors about the losses they are taking suggest that the gap between what the government is paying the contractors for the project and what it’s actually costing them to build it is let’s say a nine-figure sum, it’s in the hundreds of millions.
“That’s obviously very significant indeed.
“What the contractors think would be appropriate as a payment in order to release the bit of road that’s finished I don’t know. I think we need to know.”
He added: “We are in stalemate. The problem is the contract.
“We have heard Michael Matheson say it’s entirely the contractors who are holding this up, and if that’s the case I think parliament is right to hear from them as to why that’s happening.”
Transport Scotland said the contract for construction of the project and maintaining it for 30 years would not exceed £745m.
It would not comment on speculation about extra costs for the contractors due to commercial sensitivities.
The proposed date for the contractors giving evidence is 5 December.
No definitive date
Galliford Try said on Wednesday that the project would be completed in December, following “increased complexity” and weather delays in carrying out bridge repairs.
Mr Matheson said last week there was still no definitive date for the opening.
It was due to open in the spring but was put back to autumn.
The ongoing work is one of the biggest infrastructure projects in Scotland.
Preparatory work on the Aberdeen bypass began in August 2014, and construction work began in February 2015.