This writer should block out some time with a dictionary. Block has quite a few definitions, but not one fits here.
The writer should have used bloc, which applies to coalitions of people, groups or nations seeking the same goal. The Associated Press Stylebook takes pains to note that block doesn't apply to political alliances; however, block, according to Dictionary.com, does apply to a quantity or section taken as a unit or dealt with at one time (e.g. a large block of library card requests).
Mr. Rewrite supposes that that last definition allows those paid to know better to use voting block rather than voting bloc., since those voters aren't necessarily aligned. But the latter outnumbers the former on Google News by 9-to-1, and Mr. Rewrite recommends going with voting bloc.