It was part of the negotiations. As to what was proposed and where it ended up, I don't have a full overview, because parties presented proposals and counter-proposals, and so on. It was a process that ended up with the result you see today, with 15% for the most sensitive products and 10% for the less sensitive products. This was the result of the rather lengthy negotiations that took place on the part of the two parties making proposals to each other.
On March 31st, 2008. See this statement in context.