Britain's Office of Fair Trading (OFT) is cracking down on the popular microblogging site's high-profile users who advertise products without stating their association with the company.
A statement from the OFT says users who don't disclose endorsement deals are "deceptive", adding: "This includes comments about services and products on blogs and microblogs such as Twitter."
Hurley has served as an Estee Lauder spokesperson for 17 years and has gushed about the cosmetics range in posts on her Twitter page, while Allen has made reference to Grey Goose vodka and PlayStation.
A spokesperson for the British singer insists, "We wouldn't comment on whether it was part of a deal. It's nobody's business."