"I make no apology for the fact that we are sending out this leaflet to all households," Cameron said, as quoted by the BBC broadcaster.
According to Cameron, the leaflets were "money well spent."
"We're not neutral in this. We think it would be a bad decision to leave — for the economy, jobs, investment, family finances and universities," the prime minister added.
The government responded to the petition, initiated by the Get Britain Out campaign, which hopes to end Britain's membership of the 28-nation bloc, in January. According to the governmental statement, the leaflets are necessary so that the public is clear on "what reforms have been agreed [between London and Brussels], and what EU membership means for the UK."
At 100,000 signatures, the petition will have to be considered for debate in the UK parliament.
British nationals vote in the Brexit referendum on June 23, after Cameron negotiated a deal with 27 other EU leaders to grant the United Kingdom a special status within the bloc.