The Employers and Manufacturers' Association says changes to employment law put on hold by the Government need to be reintroduced, while the CTU wants them thrown out altogether.
With the resignation of the Act MP John Banks, the Government no longer has the numbers to pass the Employment Relations Amendment Bill.
Prime Minister John Key says the National Party would reintroduce the bill if it wins the election on 20 September election.
EMA chief executive Kim Campbell says the bill addressed important issues such as working conditions and lunchbreaks and he was confident it would reappear.
CTU vice-president Richard Wagstaff said he hoped the bill never saw the light of day again. He said it would worsen working conditions, make bargaining with employers more difficult and even restrict tea breaks.
John Banks is quitting his Epsom seat after being found found guilty last week of making a false electoral declaration after his failed 2010 Auckland mayoral campaign.
As a result, the Government loses a crucial vote in support of the bill. The Maori Party is not supporting the legislation, so the Government was relying on Banks' vote.
Mr Key said the National Party would campaign on the changes and reintroduce the legislation after the election if it is in a position to do so.