Tew said International Rugby Board rules penalised major unions in World Cup years because of changes to Test schedules and the fact that teams are not allowed to promote their sponsors during the tournament.
However, Tew has said that a decision on taking such drastic action as a boycott would not be made lightly.
"That's obviously a last resort and our style is to be consultative, collaborative and to try to work with everybody to find a solution," he told Radio New Zealand.
"It's putting pressure on the balance sheet and frankly, in the current environment, we just can't afford to run a World Cup-year loss, nor do we think it's necessary."
Tew said solutions the IRB could consider to avoid unions making a loss at World Cups include changing the tournament date or paying more money to participating unions.
The NZRU chief claimed that he had been pressuring the IRB for changes for eight years and had gone public to try to ensure the issue is finalised by 2015.