Yesterday Twitter users notified the Chicago Department of Transportation about an unpermitted closure of the Dearborn Street two-way protected bike lane and a crosswalk. To their credit, CDOT acted swiftly to shut down the illegal blockage at Randolph Street, caused by contractors working for SBC Communications.

The bike lane is one of the city’s busiest and most important because it’s the only bikeway for southbound cyclists within the Loop. Blocking the two-way lane was particularly problematic for southbound cyclists, because they didn’t have the option of merging into northbound travel lanes to get around the work site.

Cyclists who encountered the blockage yesterday morning tweeted about the problem using the #bikeCHI hashtag yesterday morning. Streetsblog reader Kevin Zolkiewicz also sent us photos of the situation, which I forwarded to CDOT. According to a CDOT staffer, the department learned about the issue via the tweets and sent an inspector to the site .

According to CDOT spokesman Mike Claffey, an electrical contractor had obtained a permit but “did not state that they would be working in the bike lane or blocking the bike lane.” The inspector shut down the work immediately, by 1:30 p.m., and ordered the crew to clear all equipment. Claffey said that the contractor Archon Construction, working for SBC Communications, was cited and wouldn’t be allowed to resume work until they provide a traffic maintenance plan.

The photos Zolkiewicz provided served to document the violation. If an administrative law judge finds the company liable for the citation, the construction company could be fined between $500 and $2,500.