Warming up the pitcher

[drvestal]

The other day I was calling a middle school game and in between innings the catcher wasn't ready to warm the pitcher up. The coach got up from the dugout and proceeded onto the field to warm the pitcher up. I told him it had to be a player with a mask and not a coach or scorekeeper (he also volunteered). Well, the coach got upset saying they have been doing this all year and it wasn't against any rule. I told him it was against the federation rules and I was not going to allow a non-player without a mask to warm up a pitcher in between innings. He complied, but wasn't happy.

After the game I went to the rule book just to double check. I know I have read it somewhere, but couldn't locate it. So, was I correct?

Thanks in advance.