Labor faces hostility from the crossbenchers whose amendments could split the party's base over support for the government's Trans-Pacific Partnership free trade agreement.
As parliament sits for the next fortnight senators from the Greens and the Centre Alliance will take advantage of Labor division over the TPP between free marketeers and its unionists.
The Centre Alliance amendments propose the commencement date be delayed until bilateral side letters are exchanged between Australia and each other party to scrap investor-state dispute causes, and mandate labour market testing before employing foreign workers.
A second set of amendments inserts a sunset clause for legislation to be repealed at the start of 2020 if the side letters aren't signed by that time.
The Greens propose similar amendments but also recommended an overhaul of the process of signing and ratifying trade agreements "to ensure genuine transparency and community consultation".
A report from the Senate inquiry into the TPP tabled last week noted some submissions claimed the agreement had been negotiated in a "secretive and undemocratic way", and that Australia's entry had not been "sufficiently considered by an independent review of its effects".
In an interview with The Guardian, Labor leader Bill Shorten acknowledged anger from some of the trade unions over the TPP but said Labor was "committed to the vote".
"It won't be everything the unions want, but there will be improvements to the system," Mr Shorten said.
"It's about how you fix the problems, and I don't want to see farmers miss out on the benefits of being an early mover on tariff reductions."
The Minerals Council of Australia called for a "speedy passage" of the legislation arguing delays in the Senate could deny Australian exporters the opportunity of a "double tariff cut" putting them at a disadvantage against international competitors.
