The changes are designed to eliminate an estimated deficit of about £8 billion, caused largely by a fall after the post-2007 financial crisis in expected investment returns.
However, that deficit may be as large as £13 billion once the USS de-risks its investment portfolio, leading to lower but more stable returns, and adjusts its longevity assumptions.
The UUK proposals will now be put to the USS Joint Negotiating Committee (JNC), which comprises an equal number of UUK and University and College Union representatives and an independent chair, on 22 October.
A JNC recommendation will later be put to the USS Trustee Board, with a formal consultation with scheme members likely to take place early in 2015.
The UCU is already balloting members in 67 universities for industrial action to oppose mooted changes to the USS, with the ballot due to close on 20 October.