Leaders of the two national football federations warned in a letter to FIFA, including president Gianni Infantino, that unilaterally sealing the "Visit Saudi'' sponsorship could "severely tarnish the reputation'' of the 32-nation tournament that starts in July.
Such a confrontation between a World Cup host and FIFA is unprecedented in recent history, and is likely to shine more attention on so-called "sportswashing'' investments by Saudi Arabia.
"We write to express our serious disappointment and concern at the news of the apparent appointment of Visit Saudi as a sponsor,'' Chris Nikou of Australia and New Zealand's Joanna Wood wrote Wednesday in the letter to FIFA seen by The Associated Press.
"We cannot express strongly enough the potential repercussions and fallout that could result of this decision.
"Australia and New Zealand, both as sovereign nations and as football associations, have for decades placed the utmost importance on gender equality, and have sought to promote these ideals around the world,'' the letter said, reminding FIFA their governments have invested hundreds of millions in the event.
Tournament organisers and government officials in both countries were said not to have been consulted, they claimed.
FIFA did not immediately respond to a request for comment.
Saudi Arabia has made progress in women's football in the past three years creating a national team and a domestic league, plus preparing a bid to host the 2026 Women's Asian Cup.
In Saudi society, however, women's freedoms are limited by strict male guardianship laws.
The "Visit Saudi'' campaign was among more than 30 sponsors at the men's World Cup in Qatar last year.
FIFA did not formally announce that deal which became apparent through pitchside advertisements when the games started in November.