Jo Swinson refused to apologise for the Liberal Democrats' "misleading" election leaflets which resemble local newspapers.
Newspaper groups across the UK have criticised the "fake" newspapers.
The leaflets resemble traditional newspapers, but is accompanied by a small line of text explaining it is a party publication.
The "newspapers" have been sent to a dozens seats with titles such as Sheffield Hallam News, York News, Wantage Constituency Observer and Cheltenham Courier.
Speaking on Good Morning Britain, Lib Dem leader Ms Swinson defended the tactic, saying it had been standard practice for "decades".
She said: "I'm a bit baffled as to why this is a story. Liberal Democrats and other parties, the Conservatives have been doing this as well, have been doing this for decades, as well as putting out leaflets in full colour."
She added: "Different people like to receive messages in different ways and all political parties employ a wide range of these methods.
"Whether it's newspapers, whether it's newsletters, whether it's emails, whether it's advertising."