In retrospect, this was inevitable:

Sadly, egg donation has less to do with altruism and more to do with the exploitation of women–particularly young women and often poor women who are usually facing large debts or just trying to make ends meet.

In fact, we contend that human egg harvesting is the newest form of human trafficking.

That's from a piece in First Things coauthored by an adjunct professor at George Washington University and the founding director of Hands Off Our Ovaries. They're calling for Congress to adopt a definition of trafficking that encompasses not only Emperor's Club employees, but anyone who buys a kidney on the black market or eggs on the gray one. Given the breadth of their definition, it seems to me that it would also include sperm donors and surrogate mothers. Actually, given the breadth of their definition, it seems to me that it would include any employment contract of which these activists do not approve.

Even if the authors restrict themselves to adult women selling ova, it's worth reflecting on the vulgarity of this conflation. Johan Hari here describes a 14-year-old Bangladeshi girl sold into prostitution in Calcutta, forced to service 10 men a day. The average American egg vendor is probably a healthy middle class college student looking for help with tuition. If you're actually concerned about child slavery, the idea of comparing the experiences of the former and the latter might well strike you as grotesque.

The authors go on to claim that justification for including egg vending is right there in the UN protocol on trafficking (Pdf). As they explain it, article three includes (emphasis mine):

acts of trafficking, which include recruitment of persons. Young women are heavily recruited for their eggs. One Google search would confirm this.
means of trafficking, such as forms of coercion, fraud, deception, the abuse of power or of a position of vulnerability, or of the giving or receiving of payments or benefits.
purposes of trafficking: exploitation, which is at the heart of trafficking, for the purpose of forced labor or services, slavery or practices similar to slavery, servitude, or the removal of organs.

Reading the agreement, I'm not convinced that this is an accurate summary. But it's telling that the authors' definition of human bondage involves the "giving or receiving of payments of benefits," which, to my knowledge, has not been a particularly common feature of slavery in the past.

My experiences as a victim of trafficking are chronicled here.