A couple who tried to back out of buying an Upper East Side condo by invoking the Interstate Land Sales Full Disclosure Act will not only lose their $510,000 deposit, but must pay the building developer $577,000 in legal fees, a Manhattan federal judge has ruled.

The law, known as ILSA, was enacted in 1968 to protect buyers of unimproved lots from misrepresentation by sellers. It requires that any agreement for sale or lease of a lot provide "a description of the lot which makes such lot clearly identifiable and which is in a form acceptable for recording by the appropriate public official responsible for maintaining land records." The law applies not only to sales of lots, but to sales of condominium units in unbuilt developments.