Definitely fiction. Upton Sinclair used fictional characters and events in 'The Jungle' to highlight and expose the harsh realities of the industry at that time.
No, it's not a true story. It's a fictional work that was based on Sinclair's research and observations of the meatpacking industry to expose its harsh conditions.
It's based on real-life conditions and experiences but isn't a strictly factual account. Sinclair fictionalized some elements to make a stronger impact.
You can start by following the standard citation format for novels. Usually, you'll need to include the author's name (Upton Sinclair), the title of the novel (The Jungle), the publication date, and the publisher.
The Jungle caused a stir and its effects included forcing the government to take action to regulate the meat industry. It also influenced public opinion on social and economic issues of the time and inspired other writers to address similar themes.