This is the case with co-worker and coworker. You can hyphenate this compound word if you'd like, or you can write as a single, unhyphenated word. In both cases, your spelling would be deemed as correct by some and incorrect by others.

Is co-workers one word or two?

That's your Quick and Dirty Tip: Although in general, fewer and fewer English words are hyphenated with each style guide and dictionary update, most style guides still recommend hyphenating “co-worker,” except The Chicago Manual of Style, which writes it as one closed up word: “coworker.”

What is the correct spelling of coworker?

Both 'co-worker' and 'coworker' are correct! Unfortunately, both 'co-worker' and 'coworker' are also incorrect! If you need to write a paper for college, or an article for publication, you may need to use 'co-worker' because this is the form preferred by the Associated Press.