Their axing as state-listed players opens the door for them to become Twenty20 gun-for-hires across the world.
Boasting 271 international appearances between them, the quartet were left out of WA's 30-player squad when it was announced on Saturday.
"Ashton, Jason and AJ will continue to be supported by our High Performance program as valued members of the WA Cricket setup," Kade Harvey, WA Cricket high performance and elite teams boss said.
"We're very happy with the balance of our list, and we believe we're well placed to continue the incredible run of success we've enjoyed in recent years."
Behrendorff took out Australia's best T20 player at the annual awards in January, but is recovering from a broken leg suffered during a freak accident at training in March.
The veteran pacer was struck on the left leg, hitting him just above the ankle.
But Behrendorff, and Stoinis and Agar, are pushing to be included in Australia's squad for the T20 World Cup in June in the United States and Caribbean.
These decisions follow Daniel Sams knocking back a NSW contract last season, as did Kane Richardson with Queensland.
David Warner will also do the same after he completes his retirement from international cricket after the T20 World Cup.
Warner called it quits from Tests and ODIs in January, fulling immersing himself in the T20 circuit around the world.
It comes after Queensland this week axed former Test players Joe Burns and Matt Kuhnemann from their contract list.
Kuhnemann played three Tests during Australia's tour of India last year but was not picked in any of the Bulls' Sheffield Shield games last season.
The left-arm spinner is expected to be signed by Tasmania, who are coming off a loss in the Shield final against the all-conquering WA team.
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