Employers are reconsidering smoking bans in light of the growing popularity of e-cigarettes, Bloomberg reports. Many companies that have banned e-cigarettes are waiting to see if the Food and Drug Administration will regulate the devices as strictly as regular cigarettes.

Some large companies, including Kraft and Walgreen, allow local managers to set rules about e-cigarettes. Exxon Mobil and General Motors allow e-cigarette use in designated smoking areas. CVS Caremark and Lowe’s ban them, while employees of Levi Strauss must go outside to use them.

Smaller companies, where bosses can monitor whether e-cigarettes are bothering co-workers, are more likely to allow their use, the article notes

Sales of e-cigarettes in the United States are expected to triple this year, to $1.5 billion. Sales are expected to double annually through 2018. By 2028, sales of e-cigarettes could surpass conventional cigarettes. Large tobacco companies, including Altria, Reynolds American and Lorillard, have gotten into the e-cigarette market.