Heidi Montag Threatens Legal Action Over Spencer Pratt's Tell-All

A Costa Rican-based company has offered TV's most annoying couple the opportunity to leave the country. Will they take it? (AP)

TMZ has learned Heidi Montag is downright furious with Spencer Pratt's new claim that he plans to write a tell-all book about her private life -- and is now threatening legal action to stop him.

We just spoke to Montag who tells us, "This is exactly why I left him ... Right now I'm looking into my legal options to stop it."

As we previously reported, Montag filed for divorce back in July -- and plans on making their split official on Valentine's Day.