Pliers for tightening parts for levelling cladding tiles, in particular for a pushing wedge and a levelling element; said pliers comprising: - a first arm, straight, having a handle on a rear end and a guide bar on a front end for the movable assembly of a supporting stop of the levelling element; - a second arm, at an angle, having a rear end provided with a handle and having a contact surface with the pushing wedge on a front end; - a rotation shaft relative to the arms (1, 2) of the pliers; and - means for fastening the supporting stop in different positions along the guide bar of the first arm; - wherein the supporting stop comprises: a passage with a height greater than the guide bar; and a shaft assembled in a longitudinal slot of the guide bar which enables a longitudinal movement of the supporting stop along the guide bar; and - wherein the means for fastening the supporting stop in several positions longitudinally spaced with respect to the guide bar are made up of a straight pawl comprising: a row of teeth defined along the guide bar, and a stop or tab assembled in the supporting stop and able to be housed between any two consecutive teeth of the guide bar; characterized in that: - the shaft assembled in the longitudinal slot of the guide bar further enables relative rotation of the supporting stop with respect to the guide bar between a fastening position, in which the stop or tab is housed between any two consecutive teeth of the guide bar, and a longitudinal movement position, in which the stop or tab is arranged spaced from an end of the teeth; and - the supporting stop further comprises a spring which acts against a supporting surface of the guide bar and tends to maintain the supporting stop in the fastening position with respect to the guide bar. - a first arm, straight, having a handle on a rear end and a guide bar on a front end for the movable assembly of a supporting stop of the levelling element; - a second arm, at an angle, having a rear end provided with a handle and having a contact surface with the pushing wedge on a front end; - a rotation shaft relative to the arms (1, 2) of the pliers; and - means for fastening the supporting stop in different positions along the guide bar of the first arm; - wherein the supporting stop comprises: a passage with a height greater than the guide bar; and a shaft assembled in a longitudinal slot of the guide bar which enables a longitudinal movement of the supporting stop along the guide bar; and - wherein the means for fastening the supporting stop in several positions longitudinally spaced with respect to the guide bar are made up of a straight pawl comprising: a row of teeth defined along the guide bar, and a stop or tab assembled in the supporting stop and able to be housed between any two consecutive teeth of the guide bar; - the shaft assembled in the longitudinal slot of the guide bar further enables relative rotation of the supporting stop with respect to the guide bar between a fastening position, in which the stop or tab is housed between any two consecutive teeth of the guide bar, and a longitudinal movement position, in which the stop or tab is arranged spaced from an end of the teeth; and - the supporting stop further comprises a spring which acts against a supporting surface of the guide bar and tends to maintain the supporting stop in the fastening position with respect to the guide bar.