The feed unit (10) comprises: a first pair of motor-driven lower rollers (12a, 12b) for moving first tubes (T1) forward along a first feed axis (x1); a second pair of motor-driven lower rollers (14a, 14b) for moving second tubes (T2) forward along a second feed axis (x2) parallel to the first one; a first pair of upper rollers (16a, 16b) for urging the first tubes (T1) against the first pair of lower rollers (12a, 12b); a second pair of upper rollers (18a, 18b) for urging the second tubes (T2) against the second pair of lower rollers (14a, 14b); a plurality of first side rollers (22) for retaining laterally the first tubes (T1); and a plurality of second side rollers (24) for retaining laterally the second tubes (T2). The upstream rollers (12a, 14a) of the first pair of lower rollers (12a, 12b) and of the second pair of lower rollers (14a, 14b) are rotatably mounted about a first transverse axis of rotation (y a ) inclined by an angle (±) to the horizontal. The downstream rollers (12b, 14b) of the first pair of lower rollers (12a, 12b) and of the second pair of lower rollers (14a, 14b) are rotatably mounted about a second transverse axis of rotation (y b ) parallel to the first one. The upstream rollers (16a, 18a) of the first pair of upper rollers (16a, 16b) and of the second pair of upper rollers (18a, 18b) are rotatably mounted about a third transverse axis of rotation (y' a ) parallel to the first one. The downstream rollers (16b, 18b) of the first pair of upper rollers (16a, 16b) and of the second pair of upper rollers (18a, 18b) are rotatably mounted about a fourth transverse axis of rotation (y' b ) parallel to the first one. Each upper roller (16a, 16b, 18a, 18b) is adapted to be moved towards a respective lower roller (12a, 12b, 14a, 14b) to clamp a respective tube (T1, T2) against the lower roller (12a, 12b, 14a, 14b). The feed unit (10) further comprises a separating element (34) movable between a rest position, in which it is not interposed between the first and second tubes (T1, T2), whereby the first and second tubes (T1, T2) are in contact with each other, and a working position, in which it is interposed between the first and second tubes (T1, T2) thus preventing these tubes from being in contact with each other.