Armed police were deployed outside V&D shops and a restaurant in the city to the west of Amsterdam after "threatening tweets" were made, police said in a statement.
The tweets were made last night saying there would be a bloodbath at a V&D shop today at 11:50 am (1520 IST), with at least 10 dead, Dutch media reported.
The author of the tweets said he or she would carry out the attack in retaliation for being fired, presumably from a V&D shop.
Several other shops in Haarlem decided to shut down while others remain open, police tweeted, as a police helicopter flew over the city.