Prime Minister BIll English says it is "hard to understand" why Sonny Bill Williams covered up a bank sponsor's logo during Saturday night's Super Rugby match between the Blues and the Highlanders.

"It is hard to understand that one guy has to behave differently than the rest," English told the AM Show on Monday.

"I don't understand all these professional contracts, but if you're in the team, you're in the team."

Bill English disagrees with SBW's logo call.

Williams used plaster tape to cover the BNZ's logo on both sides of his jersey collar as he played his first game of 15s since the 2015 World Cup final when the Blues lost to the Highlanders in Dunedin on Saturday night.

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It's understood Williams, a Muslim, has taken a religious stand on the issue of banks charging interest and fees on loans.

"Sonny Bill Williams has lodged a conscientious objection with New Zealand Rugby in his contract to finance companies, banks, alcohol companies, tobacco companies and gambling companies," NZ Rugby confirmed in a statement.

Williams has said he will "clarify the situation during the week".

In regards to my jersey during the game I'll clarify the situation during the week. — Sonny Bill Williams (@SonnyBWilliams) April 9, 2017

But that didn't stop the Prime Minister having his thoughts on the issue in his regular Monday chat with the AM Show, adding: "You wear the team jersey ... but they'll sort it out."

NZ Rugby have said it's a matter for the Blues to sort out.

The Blues host the Hurricanes in Auckland this Saturday and Williams' brief but impressive appearance in Dunedin means he is certain to be in their mix again.

The Blues are looking to address the issue with Williams' management.

The BNZ have neatly side-stepped the issue, saying they don't have a problem with Williams' stance.

"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."

IT'S HAPPENED BEFORE

It isn't the first time that a sponsor's logo has been blanked out on a sports field, particularly for religious reasons.

Good friends of Williams, South African cricketers Hashim Amla and Imran Tahir, are both Muslim and refuse to wear clothing with the Proteas' main sponsor, Castle Lager, on the jersey.

The pair have been given special dispensation to wear different uniforms to other members of the South African squad.

As such, Amla and Tahir are issued uniforms without the Castle Lager sponsorship. They do so because drinking is forbidden in Islam.

In English football, former Newcastle United striker Papiss Cisse pulled out of the club's preseason campaign over a new shirt sponsor, loan company Wonga.

Muslims must not benefit from the lending of money under Islamic law. Cisse offered to wear the logo of a charity brand instead.

Cisse ended up coming to an agreement with Newcastle in which he did wear the Wonga logo.

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