Change in Contributiion Formula--Money Purchase Plan

[KJohnson]

If contributions to a money purchase plan are not due until the end of the plan year and then only for employees employed at year end, can you reduce the contribution formula mid-year as long as you give a 204(h) notice.

I thought I read somewhere that IRS says that you cannot change the formula for anyone with over 1,000 hours at the time of the amendment. However, I cannot locate where I read this.