Val Kilmer's ex-wife claims he has failed to pay his child support.

Joanne Whalley -- who had two children, Mercedes and Jack, with the 'Batman' star before their split in 1996 -- alleges Val had fallen behind with his $27,500-per-month payments so she has now established a lien on his property to force the actor to pay up.

Although Mercedes is now 19, Jack is only 16 so Val still legally has to pay for him.

According to documents obtained by website TMZ, Joanne didn't specify how much Val owes but it seems to be quite a lot as she is seeking his $18.5 million New Mexico ranch so she can get what she claims she is rightfully owed.

In 2009, Val listed the ranch for sale for $33 million, but the price was subsequently dropped to $23 million in October 2010 and dropped again to $18.5 million two months later.

In November 2010, the Internal Revenue Service (IRS) filed a $498,165 lien against Val's ranch for unpaid 2008 income taxes.

In April 2010, Kilmer paid $538,000 to settle another dispute with the IRS.