Labour leader Jeremy Corbyn has pledged his party would repeal Conservative trade union reforms and introduce a "positive charter" for workers rights.
With the Tories having a majority in the House of Commons, he said the reality was that the Government's Trade Union Bill would be passed by MPs
But he told a rally in Glasgow: "I want us to repeal that Bill if it becomes law."
The veteran left-winger made the pledge as he addressed an event organised by the Scottish Trades Union Congress, which also heard from First Minister Nicola Sturgeon.
She pledged to raise Scotland's opposition to the legislation with David Cameron when she has talks with him in Downing Street on Monday.
Mr Corbyn told more than 1,000 activists at the city's Royal Concert Hall that Labour would oppose the proposals "with every means at our disposal", but he added: "The reality is it is likely to become law."
If passed the Bill will introduce a threshold for strike ballots, new measures on picketing and will also allow c ompanies to hire agency staff to cover for strikers.
"It is what the Tories are about, attacking the working class basis of trade unions and our organisation," the Labour leader said.
Mr Corbyn, a former trade union organiser, said he wanted a future Labour government to do more than just repeal the Conservative legislation.
His party would aim to eradicate the "scourge of in work poverty" he said, as well as "setting out a positive charter for employment rights, positive rights for workers that will apply from day one of your employment".
The Labour leader claimed moves like this would end the "exploitative casualisation of the workforce"
Earlier Ms Sturgeon had told the rally of the Scottish Government's " total unequivocal opposition to the anti Trade Union Bill".
The SNP leader said: " This Bill is not just an attack on trade union rights, in attacking trade union rights this Bill is attacking human rights be in no doubt. It is outrageous, unacceptable and completely unwarranted attack on rights and freedoms that were hard won and hard fought for by generations of workers and generations of campaigners.
"Rights and freedoms that we believed we could now take for granted, these are the rights and freedoms that are under attack by this Tory Government, a Tory Government that has got one seat in Scotland."
She pledged "each and every one" of the SNP MPs in the Commons would vote against the Bill.
The First Minister continued: " Yes we will argue that it shouldn't apply to Scotland but let me make this clear, that would be second best to it not applying anywhere. I want to express my solidarity and the solidarity of my party to trade unions in every single part of the United Kingdom.
"I'm going to meet the Prime Minister on Monday in Downing Street and I will take the message from here directly to him that Scotland opposes your anti Trade Union Bill."
She vowed the Scottish Government would "never ever employ agency workers to undermine strike action", telling the audience: " As First Minister I stand with you in solidarity in defending your rights because in defending your rights we defend all of our rights. Solidarity is what you get from this government."
The rally comes after Holyrood blocked a bid by the Scottish Government to withhold its consent for the measures to to be brought in north of the border.
Presiding Officer Tricia Marwick - Holyrood's equivalent of the Speaker of the House of Commons - said the SNP administration's attempt to use a legislative consent memorandum was is ''not competent'' in relation to the reserved Trade Union Bill.
Ms Sturgeon insisted: " This Bill should not pass unless it has the consent of the Scottish Parliament, consent that it will never ever get.
"We this week lodged in the Scottish Parliament a legislative consent memorandum seeking to start that legislative consent process. Unfortunately that has been blocked but we will continue to use everything we possibly can to make sure that our democratically elected Parliament gets its say and has its voice heard."
She argued: " This Bill impacts on devolved responsibilities, be in no doubt, it impacts on the responsibilities of the Scottish Government as an employer. It is absolutely outrageous that it can be passed in the wake of opposition from the Scottish Parliament.
"If this Bill is passed we are going to do everything in our power to make sure this Bill will not succeed. We will not stand by and let this Bill undermine the relationship we have with trade unions."