Tony Judt, in his 2005 book Postwar: A History of Europe since 1945, states that the final straw which 'forced' Slovenia to declare their independence from Yugoslavia was when, in December 1990, the Serbian leadership in Belgrade, seized, without authorization, 50% of the entire drawing rights of the Yugoslav federation to cover back pay and bonuses for state employees (p. 673).
Slovenia, which had only 8% of Yugoslavia's population and which provided roughly 25% of the federal budget, no longer felt that their national interests were served by following centralized fiscal decisions from Belgrade and thereby decided to embark on a journey towards independence.
Would you consider this account to be accurate? Were there other factors which pushed Slovenia to declare its independence from Yugoslavia? Did the Slovenian political leadership simply use this act by the Serbs as a justification for independence? And finally, why did the Serbs commit to such a reckless course of action, did Milosevic simply believe that the other republics would not break away from Yugoslavia?
I'll let someone who is better informed on the subject give the full answer to this, I just want to note that, even if it was the 'Straw which broke the camels back' its still important to realize that there were also other, much older factors involved. I'd say that the Slovenians wanted to part from Yugoslavia for quite some time but didn't have the numbers or political power to do so before the nineties when they used their chance (with the fall of Soviet Union and complete Western dominance) and successfully portrayed their situation to the rest of Europe as a matter of "David vs Goliath" to ensure that they'll be supported by them and were betting that Serbian leadership would be more concerned with the problematic situation in Bosnia and Croatia. That event in December 1990 in itself probably came in the right time to shape the pubic opinion in favor of separating (even more than it was) but it's hardly the main factor that caused the Slovenia to break the union (that was almost 82 years old at the time). And yeah, Serbia's leadership was reckless and turbulent in the nineties, many people don't realize just how chaotic was the country at the time and the leadership reflected that mess, with people like Milosevic overestimating their power and deciding stuff based on emotions and not common sense like you would expect from a country's president. Hope this helps, again, I'm no expert on this subject in particular and it's still a touchy subject but this is what I can tell you from what I've learned so far