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."