The party's leader is addressing the Scottish Trades Union Congress in Aviemore.
Labour has only one MP in Scotland, having lost 40 seats to the SNP at the last general election.
One recent poll put the party 20 percentage points behind the Conservatives in Scotland, and further behind the SNP.
Mr Corbyn said: "Labour will never, ever apologise for the closeness of our relationship with the trade union movement, you are our family.
"That is why one of the very first things we will do when forming our Labour government will be to repeal the vicious Tory Trade Union Act, giving working people the rights to collectively organise and make their lives better, safer and more content."
Introduced by former PM David Cameron, the act introduced a threshold for workers voting in strike ballots for action to be legal.
The government said it "protects millions of people from the effects of undemocratic strike action".
The SNP leader Nicola Sturgeon will also address the congress in Aviemore.
She will say the general election is "a two-horse race between the SNP and hard-line Tories".
According to a Panelbase poll for the Sunday Times in Scotland, Labour's support there stands at 13%, compared with 33% for the Conservatives and 44% for the SNP.
Scottish Conservative deputy leader Jackson Carlaw said Mr Corbyn represented a "clear and present danger to the Union".
He said: "Nicola Sturgeon is trying to use this election to push ever harder for a second referendum on independence.
"Under Jeremy Corbyn, Labour would simply roll over and let her do so."
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Labour will "never, ever apologise" for the closeness of its ties with the trade unions, Jeremy Corbyn has said.