Signs telling voters in key electorates to put the Liberals first were designed to look like they came from the independent electoral commission, a key party figure admits.

The Chinese-language signs were posted at Melbourne polling booths, including the electorates of Kooyong and Chisholm, on election day in May.

The elections of Josh Frydenberg and Gladys Liu are being challenged over these signs that appeared in their electorates.

When translated, the purple and white signs - in the colours used by the Australian Electoral Commission - say the "correct" way to vote is to put the Liberals first.

Failed Kooyong candidate Oliver Yates is challenging Treasurer Josh Frydenberg's re-election, and climate campaigner Vanessa Garbett the election of Chisolm MP Gladys Liu, alleging the signs broke the law.