A coalition of technology companies and advocacy groups earlier this week wrote to the Federal Communications Commission, urging it to open a public investigation into zero-rating practices, in which mobile providers allow some video or music providers to be excluded from data caps. The group, which includes Common Cause, Etsy, Foursquare, Mozilla and Upworthy, called on the FCC to examine the zero-rating practices of AT&T, Comcast, T-Mobile and Verizon to determine whether those practices harm competition.