The New Day Co-Op is an alliance of drug dealers which began in the third season. They share their product and try to limit violence to deter police investigation.
Believing that the police would pay less attention to the drug trade if violence were kept to a minimum, Proposition Joe and Stringer Bell reached out to all the major drug kingpins in Baltimore, with an offer. Joe will provide them with his heroin, which is directly shipped by The Greek's organization and superior to any other because it is "fresh off the boat" and, thus, more pure; in return, they will all agree to settle their differences peacefully. They run their organization by Robert's Rules of Order
. They initially come together in the episode "Straight and True".
When Avon Barksdale gets involved in a war with Marlo Stanfield in season three, the Co-Op votes to deny Stringer the high quality heroin until the violence stops. Ultimately, the Barksdale Organization dissolves. In the fourth season, Marlo joins the Co-Op. When Omar steals the shipment that Joe's men are receiving, the Co-Op decides that Joe should be responsible for replacing the lost heroin. Joe threatens to cut them all off, since he is the only one with contact with The Greek, confirming his power over the rest of them. They reluctantly agree, but Marlo makes a point of meeting Spiros Vondas, the second-in-command to the Greek.
There seem to be at least a dozen members of the Co-Op, many of whom have not been named on screen. Marlo at first does not want to join the Co-Op, but later does when Joe lets him know that he knew the poker game (where Marlo was in attendance) was going to be robbed. He aides the Co-Op in fighting off drug dealers from New York attempting to take over parts of the East Side. In return, learns from Joe how to launder money through charities and the lawyer Maurice Levy.
Proposition Joe (and his crew)
"Proposition" Joe Stewart is an Eastside drug kingpin who supplies much of Baltimore through his international connections and involvement in the new day co-op organization.
Slim Charles is a lieutenant and enforcer in Proposition Joe's organization.
Melvin "Cheese" Wagstaff
Cheese is Proposition Joe's nephew and was a lieutenant in his drug-dealing organization until he betrayed him to Marlo Stanfield.
Fat-Face Rick is an East side drug kingpin.
Kintell Williamson is a North Eastern district drug kingpin.
Phil-Boy is a drug kingpin.