The State Government may be in breach of international law by charging 457 visa scheme workers thousands of dollars to send a child to a public school because free education is deemed a right.
UNICEF and the Centre for Human Rights Education at Curtin University said the policy breached the Convention on the Rights of the Child.
Article 28 says signatories should "make primary education compulsory and available free to all" and higher education should be available where it has capacity.
The Education Department revealed it sought legal advice after the Budget announcement that skilled migrants would have to pay $4000 a year to send a child to a WA public school.
It said the advice was that the convention was not incorporated in domestic law.
UNICEF spokesman Tim O'Connor and Mary Anne Kenny, director of the Curtin centre, said this effectively meant the State could not be taken to court despite the international breach.
"The children's convention stipulates clearly that Australia, as a signatory, has an obligation to provide free access to education," Mr O'Connor said.
"UNICEF Australia would urge the WA Government to reconsider changing this policy which will disadvantage innocent children who find themselves only able to get an education if their parents can afford to pay for it."
Welsh tiler Dennis Owen said his family arrived under the 457 visa scheme shortly before the policy was announced after a Perth firm headhunted him to teach apprentices specialised tiling. It's believed he is the only such specialist in WA.
Mr Owen said his family was devastated that they might have to return to Wales because he could not afford $20,000 to send his five children to school.
He tried for a bank loan to cover the fees but was rejected.
"I sold the home, the car, the furniture and quit my job so I could come here," he said.
"We'll be returning home to nothing."
Opposition MP Stephen Dawson said the matter, straight after the solar feed-in tariff fiasco, was policymaking on the run.
He said it would force many 457 visa scheme families back home.
To meet the State Government forecast income of $35 million in its first full year of the policy next financial year, every one of the 8600 students from 457 visa scheme families would have to pay the full fee.
Education Minister Peter Collier said the School Education Act 1999 provided for overseas students to pay a "fee for instruction" at a government school.