Cameron, who was speaking at a Wine and Spirit Trade Association (WSTA) roundtable along with Environment Secretary Liz Truss earlier this month, said almost 600,000 jobs in the sector would be more secure in a reformed EU than if Brits voted to exit.
A poll of the WSTA's 300 members echoed the PM's message, the organisation claimed.
Uncertain trading environment
Concerns about a so-called Brexit included an uncertain trading environment and a loss of access to mainland Europe, where a third (£1.7bn) of the UK's wine and spirit exports go.
WSTA survey in figures:
- 90% of respondents want to stay in the EU
- 2% want to leave
- 8% are undecided
- 91% say the EU is important to wine and spirit trade
- 85% say it had a positive impact on their business
- 81% say leaving would create uncertainty
Britain would be stronger, safer and better off in a reformed Europe, said Cameron. "We will have full participation in the free trade area, bringing in jobs, investment, lower prices and financial security. That means real certainty so you can plan the future.
"On the other hand, those who want to leave Europe can't tell you if British businesses would be able to access Europe's free trade area; or if your job is safe or how much your prices would rise."
WSTA members also raised concern about the effect a vote to leave the EU would have on trade outside Europe. Losing the EU's free trade agreements with countries outside the EU could impact the £3.5bn worth of international trade, they said.
WSTA chief executive Miles Beale said: "While all views were represented in our membership, the vast majority are clear the industry will be better able to invest, grow and create jobs if the UK remains in the single market."
Powerful voice
He added: "The industry needs a powerful UK voice within the EU to ensure we can shape and influence regulations that will impact the trade and its access to the EU's 500 million consumers.
"It is clear the UK's spirits sector's strong performance and our place at the centre of the international wine industry is hugely positive for the UK and its consumers. There is real concern that this would be put at risk as a result of the UK exiting the EU."
Meanwhile, opinions about Britain's future in the EU were mixed among the licensees asked by the Publican's Morning Advertiser earlier this month. Follow the link to find out who said what.