The vote last Tuesday was 26-11 in favor of an amendment by Pittsburg Republican Jake LaTurner that would make it illegal for Kansas residents to place bets online.
Critics questioned whether the ban could be enforced.
Senators expected to vote this week on the underlying bill, which revises a 2007 law authorizing state-owned casinos and slot machines at dog and horse tracks.
The law requires a prospective developer to invest at least us$ 225 million in a southeast Kansas casino, and backers of such a project say the threshold is too high. The bill would drop it to us$ 50 million.
But the measure would repeal the authorization for racetrack slots.