Liarbanese, page-265

Just checked and seeing that it's a section 53 Bill presumably the Senate can't make amendments. They'd have to negotiate with Labor and send it back to the House of Reps for amendments there.
If they came to a stalemate then the previously legislated stage 3 tax cuts would presumably come into effect.

Money bills
The powers of the two houses to initiate and amend bills are identical except in relation to bills that impose taxation or appropriate money. Section 53 of the Constitution provides that such bills may originate only in the House of Representatives. Bills which impose taxation or appropriate money for the ordinary annual services of government may not be amended by the Senate. Thus if the Senate wishes to amend such a bill, it must request the House of Representatives to make the amendment.