The Democratic Presidential candidate and Senator from Massachusetts doubled down Tuesday morning ... adamantly saying she was shown the door at 22 from a teaching job in New Jersey just because she was visibly pregnant. It's a personal story she's told on the campaign trail in her quest to champion women and labor issues.

Warren's comments come on the heels of a report from the right-leaning website, the Washington Free Beacon ... which reported that county records show Warren resigned from her position in 1971 as a speech pathologist just 2 months after the board "unanimously approved" a "provisional certificate" that would extend her teaching contract a second year.

Warren insists that after one year of teaching, the principal told her the job promised to her would go to someone else. But, the Free Beacon, citing county records, reports Warren submitted her resignation after just one year and the board "accepted with regret."

BTW ... back in 2007, Warren explained her departure from teaching during an interview at UC Berkeley. She had said, that after a year of teaching children with disabilities, she'd gotten an "emergency certificate" because she lacked education courses.

Warren added, "I went back to graduate school and took a couple of courses in education and said, 'I don't think this is going to work out for me.'"