** Shares of Instacart CART.O are down 3.8% on Tues, with Amazon.com AMZN.O late on Monday saying it is testing ultra-fast delivery of household essentials and fresh groceries in parts of Seattle and Philadelphia

** Amazon said in a blog that the service will deliver items in about 30 minutes or less

** Also on Tues, Instacart sued New York City to block enforcement of five laws affecting the grocery delivery company, including rules governing minimum pay for app-based workers and disclosures to customers about tipping

** In November, Instacart beat analyst expectations for Q3 gross transaction value and core profit, helped by steady demand for essentials on its online grocery delivery platform and higher rev from advertising

** CART shares are down 0.7% YTD compared with a roughly 21% gain in the Nasdaq .IXIC in that period

(Reporting by Caroline Valetkevitch)

((caroline.valetkevitch@thomsonreuters.com))