Major superannuation funds could see returns from their American investments fall by nearly $3.5 billion over four years under a punitive tax regime that would target countries that the Trump administration deemed to have discriminated against businesses in the United States.

The so-called “big beautiful bill” now at the centre of recriminations between US President Donald Trump and his one-time confidant Elon Musk contains provisions that would increase taxes on investors including the major retirement savings funds if passed unchanged.