County inspectors found that roughly half the merchandise in the chain's Yorktown and Greenburgh stores wasn't marked during two visits in October. Inspectors flagged 1,564 items in all.
Administrative law judge Jay Howard imposed the maximum fine, $1,000 per item.
County officials say the price-tag law helps customers make sure their items are rung up correctly. Kmart has argued that the law is vague, and the fine is excessive.
