The business magazine - which did not have access to all of the 30 teams' financial records - estimates the NHL lost a combined $96million last season, not $224million as reported by the league.
For the 2002-03 season, in which the NHL stated losses of $273million, Forbes estimates they were actually about $123million.
The discrepancy occurred because several NHL teams aren't accounting for all their revenue, Forbes reported. The magazine said the NHL included only half of the $17million the New York Islanders got last year for cable broadcasts, for example.
"The Forbes article is factually inaccurate in numerous respects and is not based on any of the actual information that would be needed to support its claims," Bill Daly, the NHL's chief legal officer, told The Canadian Press on Friday. "It is nothing short of irresponsible journalism."
The losses are why the NHL has shut down, imposed by commissioner Gary Bettman in September following the expiration of the collective bargaining agreement with the players association.
Bettman has vowed to get "cost certainty" for clubs, a term the NHLPA says is tantamount to a salary cap and a solution it refuses to accept.
The players association countered with a luxury tax proposal that was rejected by the league.
The NHL stands by its numbers, pointing to the league-commissioned audit by former Securities & Exchange Commission chairman Arthur Levitt.
Levitt's study found NHL clubs lost $273million in 2002-03.
But Ted Saskin, the NHLPA senior director, said: "We agree with Forbes' conclusion that the NHL should show more transparency and disclose all of an owners' sources of revenue in their financial reporting. We have been saying the same thing for many years."
Forbes says it spoke with bankers, broadcast sources and league sources while studying arena leases, ticket sales and prices.
