  A coalition in a graph $G$ with vertex set $V$ consists of two disjoint sets
$V_1, V_2\subset V$ such that neither $V_1$ nor $V_2$ is a dominating set, but
the union $V_1\cup V_2$ is a dominating set in $G$. A partition of graph
vertices is called a coalition partition $\mathcal{P}$ if every non-dominating
set of $\mathcal{P}$ is a member of a coalition and every dominating set is a
single-vertex set. The coalition number $C(G)$ of a graph $G$ is the maximum
cardinality of its coalition partition. It is known that for cubic graphs
$C(G)\le 9$. The existence of cubic graphs with the maximal coalition number is
an unsolved problem. In this paper, an infinite family of cubic graphs
satisfying $C(G)=9$ is constructed.
