The service, using personal shoppers to buy and deliver alcohol as well as groceries, seemed to run uneventfully in Philadelphia and some suburbs for nearly two years.
But Instacart's decision, announced in an email to consumers Thursday, appears to follow a legal opinion issued last month by an attorney for the Liquor Control Board in response to a question by a State College alcohol-delivery service.
Rodrigo J. Diaz, the LCB's executive deputy chief counsel, wrote in a letter dated Feb. 1 that a delivery service that holds a so-called transporter-for-hire license "may not accept online orders for alcohol on its website, nor may such a licensee in any other way be involved in the sale of alcohol."
In sum, the retail customer - not a contractor for a delivery service acting as a middleman - must buy alcohol directly from the LCB and not through the service.
Under Instacart's system, a customer paid Instacart for the alcohol and an Instacart shopper bought it at a Fine Wine and Good Spirits Shop, delivering it to the customer in about an hour. Under LCB rules, the state has to be paid directly.
Delivery services have argued that retail customers in effect use their services as a proxy to buy alcohol on their behalf.
Instacart did not immediately return a request for comment, and an LCB spokeswoman offered no further information.
Sgt. Dan Steele of the Pennsylvania State Police, which enforces LCB rules, said, "Instacart was advised to cease liquor sales and review their payment procedures for all sales."
Steele said no formal enforcement occurred, as the agency expects Instacart to cooperate and to seek an opinion from the LCB for additional clarity.
Most transporters-for-hire simply deliver prepaid orders to restaurants, bars, and other businesses. Instacart, based in San Francisco, was among the first companies to obtain such a license to serve retail customers. Instacart also delivers food and other items from stores.
The LCB offers home delivery of some items but it takes three to five days.