Shields, who qualifies through his parents, will become eligible for England selection when his Super Rugby contract expires at the end of the season.
The New Zealand Rugby Union have countered that his New Zealand rugby contract takes precedence, but Brown says according to World Rugby rules, Shields will be available for England selection.
“Regulation nine is clear and understood by everybody,” Brown told The Times.
“If we find ourselves in that situation we will rely on the World Rugby regulation.”
NZR chief executive Steve Tew, though, believes “the World Rugby regulations don’t apply per se because he’s committed himself to New Zealand”.
Meanwhile, Highlanders flanker Liam Squire could miss the All Blacks’ Tests against France in June due to a setback in his recovery from a thumb injury.
Squire has been sidelined since suffering his injury in the Highlanders’ Round Five victory over the Crusaders in Dunedin and was set to return to action against the Sharks in Durban on May 5.
But Highlanders assistant coach Mark Hammett confirmed that the 27-year-old is expected to be ruled out for a further six weeks.
“He had his cast taken off and under another scan it hadn’t quite set how it was supposed to,” Hammett told Stuff.
“Unfortunately, it had to be reset, and that effectively reset the start date, as well.”
The latest setback adds to Squire’s injury woes as he also broke his thumb against the Cheetahs in Bloemfontein in 2017 and that injury ruled him out for six matches.
The Rebels face the Bulls in Pretoria on Saturday and have five more games to play before Super Rugby breaks for the international window. This means Squire will be light on game-time ahead of the three-Test series against les Bleus.