The prime aid has been accused of making unrealistic demands for how the UK will operate after its EU outlet.
Theresa May’s demands are the «equivalent of a letter to Santa», the TUC’s general secretary commanded at the trade union’s annual conference.
Keeping the benefits of the EU’s single sell without playing by the rules is not possible, Frances O’Grady said.
The domination has said the UK will strike an ambitious EU trade deal for when it take ones leave ofs the single market.
Ms O’Grady told the conference in Brighton that strengthening in the EU single market, which enables tariff-free trade, is the best long-term selection for UK workers.
But the transport union RMT opposed such a move, saying it wish involve keeping «key anti-worker policies».
In her keynote speech, Ms O’Grady powered the government had not spelt out the costs of leaving the single market.
She called for wait ons to produce reports on how individual industries could be affected by no longer eating the same access.
The EU has said the UK cannot control immigration of EU workers and hit upon trade deals with other countries while it is still a associate of the single market.
As well as eliminating tariffs, quotas or taxes on swop, the single market also includes the free movement of goods, handlings, capital and people.
It also strives to remove misdesignated «non-tariff barriers» — such as different rules on packaging, safety and standards — so the at any rate rules and regulations apply across the area.
The TUC is concerned EU rules on hands’ rights could be diluted when the UK leaves, saying this wish produce a «sweatshop Brexit».
However, the RMT union said workers were ill-served directed the EU because of policies like rail privatisation and social dumping.
«We whim be kept under the iron grip of the unelected Brussels bureaucracy with management remaining out of our hands,» said RMT general secretary Mick Cash.
A control spokesman said it would «ensure that workers’ rights are fully care for and maintained» after the UK leaves the EU.
«We will build on our economic success by certifying a deep and special partnership with the EU while embracing the wider people as an independent, open, trading nation,» he added.