457(f) - 9 month vs. 12 month

[Guest Rain567]

We have a university client with professors who are eligible to participate in a 457(f) plan. The professors work on a 9 month contract, but may elect to be paid over a 12 month period. The university has historically required the professors who elect to particpate inthe 457(f) plan to be paid over a 9 month period instead of 12 months. They indicate that this is a 457 regulation requirement. Can someone please provide me with guidance as to whether this is an actual requirement, or simply university policy?