Union Provisions in SPD

If a plan has Employer Nonelective Contributions for union employees only, does it need to be in the SPD or it okay for this contribution to only be addressed in the Collective Bargaining Agreement? The employer doesn't want the whole employee population to know that the union match is more than theirs. 

Many times I see different SPD's provided to different populations - such as when different nonelective contributions are provided to different allocation groups. The provision should probably be addressed in the CB version though.

Here's a link to the Labor department's rule about different SPDs for different classes of participants:

https://www.ecfr.gov/cgi-bin/text-idx?SID=61b245fa37ff49f3c1733d64e32ca6d5&mc=true&node=se29.9.2520_1102_64&rgn=div8

29 C.F.R. § 2520.102-4.

That makes a lot of sense.  How could it possibly be required to tell people that if they were in a different class of participants they would receive more generous benefits?  How can you do that without adversely affecting morale?

I cannot remember the exact situation, but I am pretty sure that I knew of a union plan/non-union plan situation where the non-union people got bigger benefits.  Don't want to be waiving that in front of the union people!