Dutch outfit Team LottoNL-Jumbo dismissed one rider and suspended two others for using sleeping medication not provided by the team.
Spaniard Juan Jose Lobato, 28, who joined the team this year from Movistar, had his contract terminated after “mutual consultation”.
Dutchmen Antwan Tolhoek, 23, and Pascal Eenkhoorn, 20, have been suspended for two months.
The medication did not contravene governing body doping regulations.
However, Lotto said the trio had made a “severe and unacceptable violation” of team regulations.
Tolhoek also signed for the team at the start of this year, while Eenkhoorn has enjoyed a promising career in the youth ranks and is set to turn professional with the team in 2018.