"The Internet has become a virtual bodega and a chemist's warehouse," state Sen. Jeff Klein, a Bronx Democrat, said at a Manhattan press conference.
"These are things that we can find in grocery stores and bodegas around our city, and now you can actually get them delivered to your front door."
Klein and other lawmakers sent letters to the CEOs of several Internet retailers, asking that they take down ads for the potent substances and "better monitor the classifieds."
The move comes as the state plans to increase penalties for those selling the items in stores.
"It is a dangerous, unpredictable and illegal substance and for too long unscrupulous stores and online marketplaces have profited," said City Council Speaker Melissa Mark-Viverito, who has led the fight to rid K2 from her East Harlem community.