For a long time, many of us have suspected, rightly or wrongly, that IFRA’s underlying policy agenda is primarily to support synthetic aroma chemicals at the expense of natural aromatic ingredients. This is because synthetics have attractions over natural aromatics for the major aroma industry players...They are invariably cheaper, they can sometimes be produced in-house, & they and their applications may be patentable. Their composition is constant, and unlike natural aromatic ingredients, their price stability & constancy of supply are variables which are not so subject to the vagaries of the world’s ever-changing climate.

[...] In a new departure, IFRA’s Information Letter 815 indicates that opoponax (which they claim botanically derives from ‘Commiphora Erythrea var. glabrascens Engler’ – we have reproduced their incorrect botanical formatting) does not have robust enough data to allow application of Quantitative Risk Assessment (QRA) methodology, and that there is a need for more ‘up to date’ sensitization data. IFRA claims it cannot support the required studies financially, and without these studies there is a high risk that IFRA will prohibit the material. Similarly for styrax...

— From IFRA Gives Up Supporting More Natural Aromatics: Opoponax & Styrax Next for the Chop at the Aromaconnection blog.

If you need background, you might start at IFRA proposes restrictions on use of citrus oils and IFRA proposes restrictions on use of citrus oils, part two, and work your way backwards through the links. Please feel free to comment, but I can't comment on the science or even the accuracy of the claims.