The federal opposition has warned it won’t horse-trade over the government’s planned Medicare co-payment, which looks unlikely to pass through the Senate.

Labor, the Australian Greens and the Palmer United Party have all declared they will oppose the $7 payment to see the doctor, which the coalition says will help pay for its new Medical Research Future Fund.

Prime Minister Tony Abbott says he is open to “horse-trading” to get his government’s first budget through the Senate.

But opposition health spokeswoman Catherine King dispelled any thoughts Labor may be willing to negotiate on the co-payment, which it has dubbed a “GP tax”.

“We will not horse-trade ever on an issue that means that patients, the most vulnerable Australians, will be forced to pay more for their healthcare,” she told ABC Radio on Thursday.

Linking the medical research fund to the co-payment – which will raise $3.5 billion over five years – was “entirely cynical”.

“How cynical to make people pay for it out of the back of a GP tax,” Ms King said.

Opposition leader Bill Shorten will deliver his budget reply speech in parliament on Thursday night.