The Steelbacks crushed Gladiators by six-wickets in the Twenty20 Cup earlier this week with star performances by their South African contingent.
Lewis says the Steelbacks were the better side and "thoroughly deserved" their win.
But he added: "I was disappointed to see my England colleague and friend Mony Panesar reduced to training on the outfield while a clutch of South Africans went into battle for the home side.
"I have already gone on record this season to register my disapproval of a system that allows counties to field so many non-England qualified players.
"Along with Leicestershire, Northants are perhaps the worst offenders.
"The side we faced the other night included no fewer than six South Africans, five of whom are Kolpak players. You cannot tell me that such an imbalance is in any way good for the English game.
"I was appalled to see Monty sitting on the sidelines watching while non-qualified players contested the game.
"It's disgraceful that an up-and-coming young player, who desperately wants to play one-day cricket for England, should be left out in favour of a bunch of Kolpak players.
"How can Monty not playing Twenty20 cricket possibly benefit the England team? I know for a fact that the paying spectators would have loved to see Monty in action at Campbell Park rather than players with whom they have next to no affinity."
Lewis' comments come in his column for the Bristol Evening Post. Click here to read the column in full
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