How about the Medicare Secondary Payer provisions? The 2000 Instruction booklet from HCFA has several sections highlighted in red. Some of them are:
"An employer cannot offer, subsidize, or be involved in the arrangement of a Medicare supplement policy where the law makes Medicare the secondary payer."
or
"If they reject coverage under the employer plan, you may not offer them, facilitate or subsidize a plan intended only to supplement Medicare benefits."
and lastly, here's part of the IMPORTANT WARNING
. . .. HCFA wishes to make sure that employers understand the legal consequents of purchasing directly or indirectly and individual Medicare supplement (Medigap) policy for an employee or spouse of an employee. This arrangement constitutes a GHP (group health plan) uner Medicare law and the Internal Revenue Code. . . . In addition, the plan, because it takes inaccount the Medicare entitlement of the beneificary is also a non-conforming GHP which would subject the employer to possible excise taxes.
According to the booklet, the underlying regulations are in Section 1862(B) of the Social Security Act (42 U.S.C. Section 1395y(B))and at 42 C.F.R. Part 411 (1990)