In this paper, we consider induced subgraphs of the Hamming graph H (n, 3). We show that if U Z₃ⁿ and U induces a subgraph of H (n, 3) with maximum degree at most 1 then 1. If U is disjoint from a maximum size independent set of H (n, 3) then |U| 3^n-1+1. Moreover, all such U with size 3^n-1+1 are isomorphic to each other. 2. For n 6, there exists such a U with size |U| = 3^n-1+18 and this is optimal for n = 6. 3. If U \x, x+e₁, x+2e₁\ ϕ for all x Z₃ⁿ then |U| 3^n-1 + 81. 41 pages. This is the journal version of our paper
Potechin et al. (Fri,) studied this question.