If you're a text messaging company serving thousands of clients (including Rick Warren's Saddleback Church), having your short code blocked by a wireless carrier is a death knell. But the four-year-old EZ Texting says in a new lawsuit that T-Mobile began blocking all access to its 313131 short code on September 10—all due to an EZ Texting client that provides information about medical marijuana.

At some point this year, EZ Texting says that T-Mobile got wind of legalmarijuanadispensary.com, a website which uses EZ Texting to communicate with cell phone users who want information on legal marijuana dispensaries in California. Deeply alarmed at the prospect of client messages not being passed to one of the big mobile operators, EZ Texting had cut off its relationship with the marijuana website on September 9, despite believing that it was "acceptable under all applicable laws and regulations."

On September 10, T-Mobile blocked EZ Texting's short code anyway, affecting all of the company's clients. "In other words," said the company's CEO in a separate declaration, "even when EZ Texting acceded to T-Mobile's (unreasonable and unlawful) demand simply to prevent further damage to EZ Texting's entire business, EZ Texting's short code was still blocked by T-Mobile."

T-Mobile allegedly told EZ Texting that it could only regain access to T-Mobile's network if the company created a completely new connection to T-Mobile. This is no small task; EZ Texting currently operates at several removes from T-Mobile, taking messages from clients and passing them through 4Info, which passes them to Open Market, which passes them to T-Mobile. Recreating this indirect connection would take "approximately six months and create significant, needless expense for EZ Texting."

Today, the company filed a federal lawsuit, seeking an injunction against the blockage.

The lawsuit turns on the question of content control: does T-Mobile have the right to block connections to its network based on the content being transmitted, and if so, how far do those extend? EZ Texting argues that T-Mobile is a "common carrier" under FCC regulations and is subject to the full scope of the agency's nondiscrimination rules—the same rules that prevent AT&T from refusing to complete particular calls or to stop service to people based on what they say over their phone lines.

DC advocacy group Public Knowledge, which has been on a mission against just this kind of text message blocking for some time, blasted T-Mobile.

"This case is yet another example of a totally arbitrary decision by a carrier to block text message calls between consumers and organizations they want to communicate with," said president Gigi Sohn. "The FCC should put a fast end to this blocking by issuing the ruling we asked them for three years ago."

That petition, filed back in 2007, asks the FCC to rule explicitly that text messages are covered under nondiscrimination rules and that carriers cannot exert control over them based on content. Nothing has happened on the issue since 2008.

We contacted T-Mobile, but the company did not respond by publication time.

Update: T-Mobile responds, telling Ars, "Though T-Mobile doesn’t typically comment on pending litigation, we believe it is important to clear up some of the confusion generated by EZ Texting’s allegations. Each carrier has a process to ensure that content providers like EZ Texting follow the Mobile Marketing Association’s US Consumer Best Practices Guidelines for Cross-Carrier Mobile Content Programs, as well as other regulations applicable to the mobile content business. When T-Mobile discovered that EZ Texting had not followed this process for WeedMaps - the text messaging service at issue in the lawsuit - we turned off the short code that EZ Texting was using for these services. The content of the WeedMaps service simply had nothing to do with T-Mobile’s decision."