1. The union asked its rank-and-file members to vote against the new contract that the company was offering.
2. Ted is getting promoted from the rank and file to a position in middle management. He hasn’t had much schooling, but his years among the workers have taught him enough to work his way up.

The expression comes from the military formation of soldiers side by side (rank) and one behind the other (file) forming large groups such as platoons. The expression has come to be applied to the non-management workers in a union (opt.1) or company (opt.2).