Local construction giant Tomlinson Group is demanding more than $11 million in late payments from Rideau Transit Group (RTG), the builder of Ottawa's beleaguered Confederation Line.

According to a letter dated Nov. 11 from Tomlinson to RTG — and obtained by CBC — the firm says that "in excess of $11,000,000 is past due and payable" and the total "includes more than $8,200,000 of holdback funds on work that was performed as long as four years ago."

The letter is signed by Kevin Cinq-Mars, the president of Tomlinson. A company official confirmed the letter was sent, but declined any comment.

An email sent Friday morning to RTG, the consortium that built the $2.1-billion Confederation Line, went unacknowledged.

The payment dispute is not currently before the courts. The letter demanding payment ends with the hope the issue can be resolved "without the unnecessary expense and trouble of legal proceedings."

Tomlinson is one of the largest construction firms in eastern Ontario. As the firm states on its website, it specializes in — among other things — "transportation infrastructure" like roads and highways and bridges.

The letter does not spell out the specific work Tomlinson carried out for OLRT Constructors, the construction arm of RTG. According to the construction company's website, however, it worked largely on the civic works aspects of the giant project, such as widening Highway 417 between Nicholas Street and the split and replacing the Lees Avenue bridge.

Tomlinson also performed some shoring and excavation work at the western portal of the 2.5-kilometre tunnel at Pimisi Station. According to the company's website, this work was done before the tunnelling work began.

In the short but pointed letter, Tomlinson states it "has a duty to pursue immediate payments of these funds for Tomlinson's subcontractors."

The letter also alludes to disagreements between the city and RTG, a dispute the LRT builders appear to have used as a reason not to pay Tomlinson.

"Based on meetings over the past several months regarding Tomlinson's subcontracts with OLRT, Tomlinson is not aware of any material construction-related disputes between the City of Ottawa and RTG/OLRT that justify ongoing delay(s) in payment(s)."

No one at the city responded to a request for comment Friday.

The city sent its final major cheque to RTG for building the LRT on Sept. 10. The last milestone payment was supposed to be $202 million, but the city withheld $59 million to cover costs it says it incurred because the project was more than a year late.

RTG has never said publicly if it agrees that the city is within its rights to hold back that much money.