Would-be swatting pranksters better think twice about making bogus 911 calls ... a new bill is winding its way through the Legislature that aims to put them behind bars for a long time.

This has become a huge problem in L.A. and there are no specific laws prohibiting the prank calls, although various laws can currently be used to prosecute anyone who's caught.

The new anti-swatting legislation is the brainchild of Assemblyman Mike Gatto (left) ... and it just passed its first hurdle toward becoming law ... the Assembly Public Safety Committee ... by a vote of 6-0.

If the bill becomes law ... swatters would be subject to a year in jail and a $2,000 fine ... and they could get even more time if the swatting prank results in someone getting hurt. In that case it becomes a felony.

Recent celebrity swatting victims include Justin Bieber, Diddy, Ryan Seacrest, Justin Timberlake, Tom Cruise and Rihanna.

Gatto tells TMZ, “This bill is not just about protecting folks like Justin Bieber. It’s about protecting kids playing in the street when emergency vehicles needlessly speed by."

But let's be honest ... it's really about protecting Justin Bieber.