Students at Grinnell College in Grinnell, Iowa, voted to expand a union of student dining workers to all student workers, becoming the first campuswide undergraduate student union at a private higher-learning institution in the country, according to the union.

The final vote tally was 274-54 with 38 challenged ballots. The Nov. 27 vote results still need to be certified by the National Labor Relations Board, likely in the next two weeks, before becoming final.

“We’re pleased, of course, by the...