The proposed national park runs from Eastbourne to Winchester
Supporters of an extended South Downs National Park have begun a postcard campaign to lobby the government.
Almost 250,000 cards have been printed by The South Downs Campaign (SDC), who described it as their "final big push".
The holiday-style postcards are addressed to Hilary Benn, Secretary of State for Environment, Food and Rural Affairs.
They request him to include a 371 sq km area (91,676 acres) in West Sussex and Hampshire reinstated into the scheme.
Organisers said they would distribute the postcards around the UK.
They depict the four key areas that the SDC would like to see included in the national park - the Chalk Hills, the Western Weald, Ditchling and Lewes.
A decision on the park is expected early next summer.
Robin Crane, chairman of the South Downs Campaign, said: "After all this time, we hope that we are finally getting close to the end of the process and that this will be our last big push for the national park.
"We hope that people will be inspired by the postcard and send it off to the government today.
"Now that the inspector's report has been submitted, the government needs to make a decision without further delay."