NZR boss Steve Tew told Fairfax Media a sit-down with WIlliams and the national union would be needed in due course.
"We've got an eye to it," Tew told Fairfax. "He has exercised a clause in his contract, and all the players are entitled to do that.
"We think it's an appropriate clause, but the extent to which that is done is obviously something we'll need to be discussing with [Williams' manager] Khoder [Nasser] and Sonny Bill in due course."
Williams is not the only top rugby player in New Zealand to exercise his right to not promote certain sponsors.
It is understood that others have had issues with fast-food giant KFC and have alerted New Zealand Rugby that they would rather not appear in advertisements. Even those who do have negotiated strict rules with the help of their players' association.
Some have felt that professional athletes backing a fast food company would send the wrong message when obesity, particularly among children, is becoming such an issue in New Zealand. Those that do appear in the television ads are never seen eating the product.
Tew conceded that while players' individual beliefs had to be protected, sponsors' interests also needed to be taken into account.
"They are crucial," he said. "We've obviously got some very loyal and supportive commercial partners and we'll make sure they're kept abreast of what's going on."