Yes, absolutely!
We had a case of this in Massachusetts this year in our governor's race. One of the third party candidates did so well during the first debate that all of the third-party candidates were then blocked from future debates. Of course, there's nothing exactly admitting that, but it seems like it could hardly be a coincidence. (In fact, the third-party candidate that did well was _uninvited_ from a future debate that he had already accepted an invitation to.)
Bonus: he ended up earning the minimum 5% vote needed to establish a new political party[0] in the state!