A US clampdown has begun on Seattle coffee shops which hire young women to serve up espressos while wearing as little as a G-string.

Officials are taking a closer look at the "sexpresso" craze after police investigations revealed some of the "bikini baristas" - set up three years ago - were serving coffee with a side of something not even legal at many strip clubs.

Five bikini baristas in Everett, north of Seattle, are accused of charging up to $80 to let customers fondle or photograph them as they put on erotic shows -- sometimes in view of passing traffic. They face court dates on prostitution charges this month.

In images so graphic that officials were reluctant to release them under public disclosure requests, undercover officers photographed them spreading their legs while wearing crotchless panties or licking whipped cream off each other's exposed pubic regions. While such acts may not constitute traditional prostitution, authorities say they met the legal definition of engaging in sexual conduct for a fee.

"This is not Malibu Barbie standing at a coffee stand selling coffee," said City of Everett spokeswoman Kate Reardon. "We had citations for prostitution. That's totally different."

The bikini barista trend emerged in recent years as some espresso stands sought to stand out amid the heavy competition for coffee business in a region that is home to Starbucks.

There are now dozens of such shops in the region, with names like Brewlesque, Twin Perks and Java Juggs. They're typically stand-alone shacks along roadsides or in parking lots, often noticeable for their come-hither signs -- "some like it hot," for example -- and a long line of pick-up trucks at the window.

The bikini shops have always stirred up controversy, with some cities threatening to shut them down unless their employees covered up. But communities have changed their laws in recent months in response to growing complaints that the bikini baristas aren't actually wearing bikinis anymore.

Snohomish County north of Seattle last month began requiring coffee stand employees to wear at least the equivalent of a bikini or face regulation under adult entertainment ordinances. That would mean tougher zoning restrictions and rules requiring customers to all be adults.

The city of Lynnwood has updated its laws to require employees to wear more than pasties and a G-string, and Yakima in central Washington directed its city attorney to draft similar laws. Everett still allows pasties, but has clarified that drive-through businesses are public places, where the caressing or fondling of the genitals or breasts is considered lewd conduct and can be prosecuted.