Bloc means a group of nations or people united by common interest. It has no other meanings. The much broader block has a variety of definitions, but a group working together is not one of them.
Examples
For example, block would bear replacement with bloc in these sentences:
Blatter will receive a fourth term in office amid rumors of the 46-member Asian voting block walking out of the meeting. [Star-Ledger]
Adopted back in 1974, this amendment introduced sanctions against the Soviet Union and other countries of the Communist block … [The Voice of Russia]
Palestine and Israel – along with Jordan, Egypt, Turkey Syria and Lebanon, are the basis for a new economic block that could grow as time moves on into the 21st century. [Milford Daily News]
And these writers demonstrate correct usage of bloc:
… British shareholders make up an important voting bloc on the company board. [Guardian]
NATO members in the ex-communist bloc are wary of moves to bring Russia on board in an anti-missile system. [The Australian]
Europe’s economic bloc has played an important role in driving global copper consumption … [Wall Street Journal]
