For a reversible system, when the pressure of the reacting system in equilibrium is increased then
the reaction shifts in the direction of a lesser number of molecules.
Pressure is one of the factors which affects the chemical equilibrium of the reversible system. If the pressure of the reacting species is increased then as per Le Chatelier's principle, equilibrium shifts to reduce the pressure. The side of the reaction with a fewer number of gas molecules will be favored. If the pressure of the reacting species is decreased then as per Le Chatelier's principle equilibrium shifts to increase the pressure. The side of the reaction with more number of gas molecules will be favored.