Prospective parents who are unmarried, over 50 or obese will not be able to adopt children from China under new rules, US adoption agencies say.
Demand for adopted children has exceeded supply
China has yet to confirm the details, but several adoption agencies say they learned of the changes - to be introduced on 1 May - a few days ago.
One US adoption agency said up to 25% of its clients could be affected.
China is a popular choice for people adopting from abroad, and has seen a surge in applications in recent years.
Those who qualify under the new rules are parents aged between 30 and 50 years, who are married and have had no more than two divorces between them, US adoption agencies said.
CHINA ADOPTION RULE CHANGES
Each parent must be between 30 and 50 years of age
Only married couples are eligible
The total number of divorces/annulments per couple is two
Families whose income is derived from retirement, disability, or insurance settlement are disqualified
No family can have more than five children in the home
Both parents must have BMI's under 40
Either parent taking medication for anxiety or depression are disqualified
From Harrar's Adoption International Mission website
Gay couples, people taking medication for anxiety and depression, and those with a body mass index (BMI) - the measure of a person's weight relative to height - of more than 40 will be excluded.
Texas-based Harrar's Adoption International Mission, which published details of the changes on its website, said up to a quarter of its families may now be disqualified.
"A large number of our families turn to adoption later in life, and applying a new rule that neither parent can be over 50 years old will disallow them... as will rules applying to obesity and number and length of marriages," Jackie Harrar, executive director, said.
Salome Lamarche, of the Indiana-based Families Thru International Adoption, said she feared the ban on those taking medication for anxiety would affect many.
She said her agency was still taking in the news so it was hard to gauge its impact. "But I think it will have an effect, though I'm unsure at this stage to what extent".
US OVERSEAS ADOPTIONS
China most popular source of US overseas adoptions since 2000
6,493 visas issued for Chinese orphans in fiscal 2006
Guatemala second most popular in 2006, with 4,135 visas
Russia third, with 3,706
Source: US state department
Both agencies said they hoped to be able to push through as many applications before the 1 May deadline.
China is a popular destination for foreign couples who want to adopt. The US approved more than 7,000 visas for children being adopted from China in 2005.
But demand has exceeded supply in recent years.
""The number of people applying for adoptions is soaring, but following the development of China's economy and society the number of abandoned and orphaned children is less and less," an official at the China Centre for Adoption Affairs (CCAA) said.
The official told Reuters news agency a formal notice of the changes would be given to adoption agencies "with which we have cooperative agreements" possibly within the week.
Ms Harrar said that, despite its impact on her clients, she believed China was acting in good faith.
"I truly believe the CCAA is doing what they believe in their hearts to be in the very best interest of these children," she told the BBC News website.