The District of Columbia (D.C.) is only able to to elect non-voting delegates in Congress, yet residents are subject to all federal laws enacted by Congress, including paying federal income tax ( i.e. "taxation without representation").
The most recent action was in 2013, where a bill, giving D.C. congressional voting rights, reached the House's Subcommittee on the Constitution And Civil Justice, but was ignored by Republican Subcommittee Chair, Trent Franks. D.C. is primarily Democrat, so of course it is in the Republican's own party's interest to keep more Democrat representation out of Congress.
Please encourage passage of this bill to give unrepresented citizens a voice in federal decisions.