The mysterious move sent social media into a flurry, with hundreds of Twitter users asking why?
The powerful 31-year-old midfielder is the only Blues player on the field to have covered the BNZ logo.
This is Williams' first 15s rugby game since the 2015 Rugby World Cup final.
Williams suffered an Achilles injury during the New Zealand Sevens team's opening pool match at the Olympics against Japan in Rio de Janeiro eight months ago.
The Herald have contacted the Blues for comment this evening.
Williams' manger Khoder Nasser said he is yet to discuss the decision with the player.
Williams converted to Islam in 2009, a religion which frowns upon borrowing money or paying interest to banks.
The rules surrounding money lending lie in the principles of Islam's shariah law.
As a matter of faith, a Muslim is not allowed to benefit from lending or receiving money, meaning earning interest is disallowed.
Boxer Anthony Mundine borrowed $500,000 from Williams before his fight against Danny Green in February, to deal with a family emergency, the Daily Telegraph reported.
The deal was sealed with little more than a handshake between two long-term friends.
Mundine gave the Blues player $750,000 in 2008 when he stormed out from the Canterbury Bulldogs to play French rugby union.
A BNZ spokewoman said the bank had no issue with their logo being covered up.
"It's really between him and the Blues - we've got no issue with it," she said.
"He's entitled to have religious beliefs and customs around that and it's really between him and the Blues as to how that manifests itself. So we have no issue with it."
Williams is not the first sports star to have refused sponsorship on his uniform.
Pakistani-born Australian cricketer Fawad Ahmed has refused to wear the team's shirt which had a VB beer logo on it. Australian batsman Usman Khawaja followed suit and had his cricket gear modified to not show the VB or XXXX beer logos, according to The Courier Mail.
Prior to tonight's match Williams shared a photo of his jersey on social media. The personalised jersey is embroidered with the names of his wife Alana and two daughters Imaan and Aisha.
