StemPAC is the most aggressive stem cell lobbying organization. Writes Roll Call in its profile of the group:

According to Roll Call, the group is “threatening to make the [embryonic stem cell] debate less about the science of the issue and more about the political ramifications” for legislators who oppose broad federal funding for the research. Hli nko says the group will push to form a nationwide grassroots campaign devoted to pressuring wavering lawmakers to support stem cell research using unused embryos created for fertility procedures that otherwise would be destroyed or discarded. StemPAC’s strategy differs “significantly” from other groups that promote embryonic stem cell research, such as the Republican Main Street Partnership.