Bank of England governor Mervyn King will address the TUC later – only the second holder of the post to do so in the union umbrella group’s 142 years.
He is also expected to answer questions from congress delegates in Manchester, who have voiced concerns this week about government spending cuts.
RMT transport union leader Bob Crow is boycotting the speech, saying Mr King is “not welcome”.
But the governor has said he will not be an “apologist for this City”.
The TUC congress has heard strong criticism of the Conservative-Liberal Democrat coalition’s economic policies, with delegates voting on Monday for joint industrial action if “attacks” on jobs, pensions and public services go ahead.
On Wednesday, the congress will also vote on plans to set up a “shadow commission” to monitor the salaries of the highest-paid company workers, similar to that established by the government to look into public sector wages.
Mr King has previously called for “decisive action” to cut the government’s £155bn budget deficit.
Deputy Prime Minister Nick Clegg has cited the governor’s advice as having been key to his Liberal Democrat party changing its approach to spending cuts, during the period in May when it was negotiating the coalition agreement with the Conservatives.
Mr King has denied that he passed any new information to Mr Clegg at the time.
However, some trade unionists blame Mr King for helping to usher in a cuts programme they regard as unnecessary and counter-productive, but which ministers say is vital for safeguarding the UK’s economic future.
Mr King is expected to seek to calm union concerns when he speaks on Wednesday.
In a pre-congress interview with the TUC’s magazine, he said: “The unions have made concessions during previous recessions, so why should they suffer now?
“The role of the Bank of England changed with independence. It was an apologist for the City. I now see it serving the nation as a whole.”
But, speaking to the BBC at the weekend, Mr Crow said: “My view is that he shouldn’t be there.
“I would like to see a single unemployed person write a two-page document about how it’s hard to survive on £67 a week, not the governor of the Bank of England tell us why we have got to pull our belt in.”
The only other occasion on which a Bank of England governor has spoken to a TUC congress was in 1998, when Eddie George did so.
No member of the government will address the gathering this year. Prime Minister David Cameron turned down an invitation because it would have clashed with his paternity leave.
Business Secretary Vince Cable had been due to attend but his invitation was withdraw in July.
This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.