In November 2012, SAS filed a formal complaint to Scandinavian aviation authorities alleging that Ryanair provides inaccurate aircraft weight figures to European aviation agency Eurocontrol, the Danish business newspaper Berlingske Business reported.
The take-off weight figures are used to calculate landing fees.
"We clearly don't think it's appropriate for Ryanair to circumvent the rules in order to get off cheaper, leaving us and other airlines that follow the rules to pay the bill," SAS spokesman Lars Andersen told Berlingske Business.
Air France has also accused the budget airline of misreporting the take-off weight.
And in Germany, Ryanair is the subject of probe by civil aviation authorities who suspected the carrier has falsified aircraft take-off weight to the tune of €370,000 ($482,000) outstanding fees per year, the Die Welt newspaper reported.
In a statement issued to The Local on Monday, Ryanair refused to comment on the substance of the SAS allegations.
“Ryanair has a policy of not commenting on rumour or speculation. There is no truth to these claims. Ryanair's 737 aircraft operate [at different certified weights] in full compliance with Boeing's flex-weight programme, as certified and approved by the Irish Aviation Authority (IAA),” spokesman Stephen Mcnamara said.