West Australian Liberal senator Chris Back has said voters told him they would back the Liberal Party in the lower house but not the Senate, in the hope the Government's superannuation changes would be blocked.

"There were certainly people who said to me we will vote Liberal in the House of Representatives but we won't support you in the Senate," Senator Back said.

The party's base made its anger over the policy known as soon as the budget came down.

The fiercest opposition is directed at the plan for a $500,000 lifetime cap on after tax superannuation contributions, back-dated to 2007.

"Dyed-in-the-wool Liberal voters said to me they were very, very upset by the suggestion that something backdated to 2007 was not retrospective, they felt insulted by that comment," Senator Back said.

Some MPs have reported unhappiness with the proposed $1.6 million cap on the amount of money that can be held in a tax-free retirement phase account by people 60 and over.

But Senator Back said he did not get that feedback.

"The overwhelming view was that the $1.6 million cap was fair and reasonable, I didn't hear any adverse comment about that. I did hear people say the $500,000 cap seemed to be unfair," he said.

Managing director of financial advice at Dixon Advisory, Nerida Cole, who advises people who self-manage their superannuation funds, warned retirees may rush investment decisions to avoid penalties because of the $500,000 cap.

"If people have already gone over that limit prior to May 3 when the change was announced they won't be penalised for those previous contributions that exceeded that limit," she said.

"But now going forward from May 3, 2016, if they make a contribution that is in excess of that lifetime limit and assuming the legislation is passed, then that would face a punitive system."

Ms Cole said the Government needed to provide certainty.

"Members need to actually go back and get nine years of historical data to assess whether they can make a contribution now, and that's actually very difficult to do when you consider that people don't need to keep their tax return and financial data for usually more than five years," she said.

Senator Back hopes next week's Coalition party room meeting will offer some hope of relief for worried retirees.

"I look forward to a debate on Monday and indeed I can understand the position of the leadership team, saying we have got to make these savings, and they do," he said.

"The challenge I think has been put out by the Prime Minister and the Treasurer to say well, if we are to make changes, come forward with where you believe there are other savings to be made and I am sure that there will be colleagues who will come forward with those suggestions."