The National Health and Medical Research Council has written to all IVF clinics around Australia advising it is aware that "a number" of clinics are offering set payments to egg and sperm donors.

The council has warned clinics set payments for donations can constitute "valuable consideration", or an inducement. This is illegal under the federal law, and can be punishable by a 15-year jail term. IVF clinics are only allowed to reimburse individual donors for "reasonable expenses" incurred as a result of their donation.

"Payment of a predetermined amount to all donors, without any consideration of individual circumstances, may constitute valuable consideration if the amount exceeds the reasonable expenses incurred by the individual during the donation process," NHMRC executive director Samantha Robertson wrote to the clinics.

The three big IVF clinics, IVF Australia, Genea and Monash IVF all told Fairfax Media they did not provide set payments to donors. They said they reimbursed expenses, such as lost wages and travel costs, on a case-by-case basis.

However an online search revealed some smaller clinics offer flat payments of $100-$200 for donors. "If a clinic offers a set amount per donation, without consideration of the donor's particular circumstances, this could leave some donors out of pocket while being sufficient to provide an inducement for others to donate," an NHMRC spokesperson said.

Demand for donor eggs and sperm is high, but supply is low, which could be prompting some operators to offer financial inducements.

"NHMRC recognises the need for gamete donation in Australia, and understands the desire to improve access to Australian donors," Ms Robertson wrote to clinics. "However, it is important that any relevant processes to do so are compliant with Australian law and practice."

IVF Australia medical director Peter Illingworth said sperm donors were unlikely to be reimbursed more than $200 in total, while costs repaid to egg donors can run to more than $1000.

Professor Illingworth said the law was so vague as to what constituted "valuable consideration" that clinics could be making set payments "quite legally". He said it would be better if the law was amended so expenses, which were allowed to be reimbursed, were itemised.

Donor conception advocates were aghast at the implications of the NHMRC letter that some clinics were paying for sperm and eggs. "We don't allow adoptions to involve payment for a child. We definitely do not allow payment for a donated organ. We don't even pay someone for donating blood," advocate Geraldine Hewitt said.

"Why then are we allowing IVF clinics to incentivise the relinquishment of sperm, eggs and embryos, which equates to a human life being disconnected from their parents ... cultural heritage [and] medical history."