The TUC has called on the prime minister to press ahead with her commitment to have workers on company boards.
The union organisation said a new law should apply to all firms with workforces of more than 250, and could be phased in gradually, starting with larger businesses.
In a report, the TUC calls for a third of company board members to be worker representatives, saying they should be directly elected by their colleagues, as happens in 12 other EU member states.
It argued that the current approach of relying on shareholders to hold companies to account has not delivered economic success or social justice.
General secretary Frances O'Grady said: "The TUC stands ready to work with Theresa May to make workers on boards a reality. If the political will is there, this policy can be on the statute books within a year.
"These are common sense plans. Those on the shop floor have a clear interest in the long-term success of their companies and deserve a bigger say.
"Seats for the workforce on company boards would do much to improve the reputation of corporate Britain. It is essential the Prime Minister holds her nerve and resists any calls to water down the proposals."
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The TUC Congress has voted to hold a co-ordinated day of national action against the Trade Union Bill.
The bill, which would tighten rules on strike ballots in Britain, passed its first major parliamentary hurdle on Monday when MPs passed it by 33 votes at the second reading stage.
Unite leader Len McCluskey told the conference in Brighton that his union will oppose the bill using "any means necessary" to defend the democratic rights and freedoms of workers.
He said: "This Prime Minister seeks to paint the millions of trade unionists and their families as 'the enemy within', with a Tory party drunk on class prejudice, intent on destroying this movement as a force in British life."
If made law, the bill would introduce a new 50% threshold on participation in strike ballots, as well as changes requiring picketers to give their names to police.
A union has welcomed Conservative plans to give emplyess three days paid leave to take part in voluntary wor.
The TUC said that members would be able to use the time to get more involved in their union.
The TUC has long called for a Community Day Bank Holiday to encourage volunteering and community engagement. We therefore welcome any move that makes employers recognise the benefits of volunteering and social action.
Trade unions are the UK's biggest voluntary groups. This new right will give every union member a guaranteed three days for time off to get involved with union activities.
At a TUC demonstration outside King's Cross, Manuel Cortes, leader of the TSSA transport union, said:
Wage rises are just not keeping up with fare rises. We have the highest fares in Europe.
People are forking out a large slice of their disposable income on fares.
Also, we are not encouraging the turn-up-and-go-railway because if you pay on the day the ticket price is very high.
TUC general secretary Frances O'Grady said:
Employment tribunal fees have been a huge victory for Britain's worst bosses.
By charging up-front fees for harassment and abuse claims the Government has made it easier for bad employers to get away with the most appalling behaviour.
Tribunal fees are part of a wider campaign to get rid of workers' basic rights. The consequence has been to price low-paid and vulnerable people out of justice.
Introducing fees for employment tribunals has been a "huge victory" for the country's worst bosses and has led to a collapse in the number of claims, according to a new report.
The TUC said women and low-paid workers had been worst affected since the Government brought in fees of up to £1,200 last year.
The total number of claims had fallen by 79%, but there had been an 80% cut in sex discrimination claims, while cases of unpaid wages and holiday pay were down by 85%, a study found.