The Dutch gynaecologists association, NVOG, has urged clinics to cease using the men's sperm immediately.
It said it found out about the two men after being tipped off by a group of single mothers. The association declined to provide further details.
In May the head of a Dutch fertility clinic was accused of using his own sperm rather that of donors to father around 60 children.
Jan Karbaat, who died aged 89 in April, ran one of Holland's largest sperm banks and billed himself as "a pioneer in the field of fertilisation".
Earlier this year a Dutch court was asked by 23 parents and children born through IVF treatment at the Bijdorp medical centre to carry out tests on Karbaat's DNA.
This article originally appeared on the Daily Telegraph.