Place bacon in a large skillet. Cook over medium-high heat until evenly brown. Drain, crumble, and set aside.
In a small bowl, mix the cream cheese with mayonnaise until smooth. Stir in Swiss cheese, onions, and bacon. Place bowl in microwave, and cook 2 minutes. Remove, and stir well. Return to microwave, and cook 2 to 4 minutes more. Sprinkle crushed crackers on top. Serve warm with crackers.