Managers said they could "no longer justify spending £40,000 per year to support staff car parking".
The changes would further prioritise clinical services funding, it sad.
But Stuart Roden, from Unison, said some staff had described the measure as a "kick in the teeth".
"For some of our members they're going to have a 1000% increase in the charges they have to pay.
"Many are low paid or part-time.  This is not going to help morale."
Mr Roden said the "blanket increase" meant staff on low wages would be paying the same to park as those on higher salaries.
Listeners opposed to the rises posted comments on BBC Radio Cornwall's Facebook page comments as "shocking", "disgusting" and "unbelievable".
But Lezli Boswell, chief executive at the RCHT, said: "We have kept the costs below those of other NHS Trusts in the region and fixed the parking charges on our site for three years but recognise that any increase will not be popular.
"The main reason for the increase is that the trust has decided to stop the subsidy we provide to staff for car parking and Cornwall Council has decided to remove the concessionary priced Park & Ride permits available to hospital staff."
From 1 October, the annual Park and Ride permits will cost £240 - with no subsidy provided.
Ms Boswell said it was "an extremely difficult decision" but the trust was facing "significant financial challenges".
Rises in staff parking charges at the Royal Cornwall Hospital (RCHT) have been criticised by Unison who say low-paid workers could face a bill of more than £300.