Bulk means (1) size, mass, or volume, (2) a large mass or matter, (3) the major portion, (4) to cause to swell or expand, and (5) being in large mass or quantity. The less common balk, usually a verb, means primarily to stop short and refuse to go on. It’s usually followed by the preposition at, though several other prepositions work. Baulk is a British variant of balk. In British publications, balk and baulk are used interchangeably, and both spellings appear about equally often. Canadian writers favor balk, and Australians favor baulk.
Examples
American and Canadian writers use balk—for example:
Like any parent, I get frustrated when my kids refuse to eat their broccoli and balk at even tasting pomegranate … [Washington Post]
At present, U.S. politicians would certainly balk at that. [Ottawa Sun]
Some British publications favor baulk—for example:
While most Britons would baulk at the prices, Nadine has become accustomed to Switzerland’s high cost of living. [Telegraph]
The grooves around which Wretch strings his stories don’t baulk at bearing out the stark messages. [Independent]
Others use balk:
It is a perennial pastime of young people, almost a rite of passage, to balk at authority figures. [Guardian]
[N]ear-zero bank deposit rates limit the choice for investors who may start to balk at chancing exposure to foreign currencies. [Financial Times]