Little Known US Open Cup Rule

Tonight is the first MLS qualifying match (LA-COL). No, it's not part of the final tournament, so I'll be saving my preview for later. But I wanted to bring your attention to something I found out last year. It was listed in last year's US Open Cup handbook, and I'm assuming that it's still in effect for this year. That would be the rule that a team can only have 5 international players in its gameday 18 for US Open Cup matches. I'm not sure if any teams would be significantly affected by this rule, but it may help contribute to the decision by teams to rest some players.