There’s ever-mounting pressure on the AEC to get Saturday’s re-run WA Senate election process right after another ballot box bungle.

There’s concern about the handling of the re-run West Australian Senate election after a fresh bungle by the Australian Electoral Commission.

About 75 pre-poll votes at the RAAFA Estate retirement home in Merriwa, in Perth’s outer suburbs, were put in an unsecured ballot box and then transferred to a secure box in breach of proper procedure.

The Australian Electoral Commission (AEC) obtained legal advice about Monday’s incident and officially informed parties on Thursday.

The Liberal Party said it became aware of the error on Tuesday and sought urgent clarification.

The retirement home’s elderly residents will have to recast their votes via a mobile AEC team.

“Those affected voters are considered to have not voted in this election,” the AEC said in a statement.

It said there was a problem with the construction of the ballot box and the mobile team’s temporary solution was later found not to be sufficiently secure.

The Liberals said it was a “serious issue”.

“If this problem occurs again on Saturday, this remedy will not be available,” the party said in a statement.

“This calls into sharp focus the need for better training of AEC staff and better management.”

Opposition leader Bill Shorten indicated he was concerned but said he was not going to panic.

“I sincerely hope that we get this process right because I don’t think anyone would be impressed by losing votes or contaminating votes on a second separate occasion,” Mr Shorten told ABC radio.

Greens senator Scott Ludlam said the incident was worrying in light of the expense and inconvenience of having a re-run poll after the AEC lost 1370 votes during last year’s recount.

“Every West Australian would be calling on the AEC to take care of the ballot papers this time, please, so we have an election people can have confidence in,” Senator Ludlam told ABC radio.

Clive Palmer raised concerns that the re-run election might not yield a valid result.

The Palmer United Party (PUP) leader said he was bitterly disappointed by the error and said it highlighted inadequacies of the AEC, which needed urgent reform.

Mr Palmer said there are no guarantee of avoiding another debacle and renewed his call for measures to reduce electoral fraud such as ensuring voters are registered with proper identification.

The AEC was lashed by Mick Keelty after his investigation into the lost votes, with the former police commissioner finding fault with just about every aspect of AEC’s handling of the recount.

Electoral Commissioner Ed Killesteyn and AEC manager for WA Peter Kramer resigned over the debacle.

AEC spokesman Phil Diak said on Thursday that every step would be taken to minimise the chances of mistakes.

Liberal senate candidate Linda Reynolds said it was important the AEC got the process right.

“It is a complete disgrace and it is very unfortunate this has happened again,” Ms Reynolds told ABC television on Thursday.

She said the incident had cast doubt on the AEC’s ability to conduct the election.