A mailman who admitted making about $35,000 selling undelivered coupons wants $25 million-plus from JCPenney for blowing the whistle on his scheme.

Thomas Tang is suing the retail giant and Nassau County, despite pleading guilty to petit larceny for making off with thousands of coupons and peddling them online.

In his Queens Supreme Court suit, Tang claims Penney falsely told the cops that it lost more than $100,000 when he “engaged in a scheme to steal JCP discount coupons out of the mail and sell them on eBay.”

Tang, 41, of Baldwin, LI, maintains that he merely took bulk-mail coupons that were tossed in a post office’s “undeliverable” bin ahead of their being “destroyed or otherwise disposed of,” because “third-class mail that is undeliverable is not sent back to the return address.”