The New York Stock Exchange suspended trading in troubled trucking company Celadon Group Inc. on Tuesday and moved to remove the company’s stock listing after Celadon said an internal investigation had identified accounting errors requiring it to restate financial results dating back to 2014. The finances of the Indianapolis-based firm, one of North America’s largest truckload carriers, have been under scrutiny over a joint venture involving its leasing division. That business foundered as the U.S. freight market stalled in late 2015 and 2016. Celadon hasn’t publicly reported earnings since last year, when it said financial statements covering more than a year couldn’t be relied on after its auditor withdrew reports for that period. The company has been negotiating with lenders as a new executive team pursues a refinancing plan to boost liquidity. Trading in Celadon’s stock was halted after the company announced late Monday it would be unable to resolve the reporting delinquencies by the May 2 deadline. The stock, which reached close to $30 a share a little more than three years ago, closed at $3.45 per share on Monday. Chief Executive Paul Svindland, who joined last year, said he was “disappointed” to learn the accounting problems extended further than previously thought but said the company was committed to accurate, transparent financial reporting. Celadon confirmed in October it was under investigation by the Securities and Exchange Commission. Mr. Svindland said Tuesday the company was "doing everything possible to cooperate with the SEC." The company has since disposed of the leasing division at the root of the accounting issues, Mr. Svindland said, and Celadon is now focused on improving its core truckload business. "The business that created the problems, we are now out of," he said.

Over the past year, Celadon has scaled back its domestic truckload division's fleet by about 20% and is reducing the number of lanes it serves from nearly 5,000 a year ago to about 1,000, said Thom Albrecht, Celadon's chief financial and strategy officer. The additional restatements are expected to result in multi-million-dollar adjustments to Celadon's balance sheet over three and a half years. The projected changes include a roughly $20 million write-down on equipment that was bought and sold at above-market prices, as well as a reduction in pre-tax net income of between $200 million and $250 million over the three years ending June 30, 2016. The company is also reviewing the impact for the first two quarters of fiscal 2017. "The cumulative effect of the adjustments, along with operating losses and other expenses since the company's last filed financial reports, are expected to reduce its reported stockholders' equity materially," Celadon said in its statement issued Monday after market close. Mr. Svindland said the carrier was working with its lenders on a new $100-million asset-based revolving credit facility. The parties are also reviewing a refinancing proposal received March 31 that includes about $200 million of term debt. The carrier had about $380.5 million in total debt as of December 2016, the latest date for which figures are available, and about $136.7 million in liquidity, according to FactSet. Mr. Svindland declined to disclose Celadon's current financial state, but said the firm is "comfortable with our liquidity." Celadon has engaged advisers during its credit negotiations with the banks to help it comply with requirements including weekly updates on the business, and to identify potential outside lenders, Mr. Albrecht said. Mr. Svindland said restructuring through a bankruptcy proceeding is "not an option." Write to Jennifer Smith at jennifer.smith@wsj.com.