Why 'groups' command shows different result in 'cron' and interactive in NIS environment?

Issue

• Command groups shows differences in cron, at and CLI.
  When groups is run from the command line expected list of groups is displayed:

$ groups
testuser nisgroup1 nisgroup2 nisgroup3

When command groups is run from at or cron for the same user, the result lacks the NIS groups:

Date: Mon, 16 Mar 2015 13:28:34 +0100
From: testuser@server
To: testuser@server
Subject: Output from your job       10

testuser