More than a rumor, some Confederate sources confirm that Blacks were indeed taken in Pennsylvania, but perhaps no more than a few dozen by inference. Typically they were claimed to have been runaways from the South, but that's very unlikely, at least in some instances. But I don't see it as an official policy, otherwise many more would have been taken south into bondage. On the other hand, most Blacks in Pennsylvania fled from the path of Lee's army, which clearly reveals their great fear.
The Confederate high command did make a clear point of destroying Thaddeus Stevens' iron works in Pennsylvania.
Here are three pertinent sources - this topic has been well covered in other threads.
- (Account of Alfred Zachry, 3rd Georgia) At Thad Stevens Iron Works, Sutler Allen Dyer of the 3rd Georgia arrested a negro here as a contraband, supposed to be a slave. Gen. Wright directed that he should be turned over to the provost guard with the other prisoners. His name was William Brown, and he said that he was a native of Pennsylvania. From personal knowledge of southern negroes, I believed his story, but we had to be troubled with him, and see that he did not escape. Prisoners were tied with a cord and led by the guard over gullies, ditches, through running streams and mud holes and all sorts of bad places.
- (Journal of Joseph C. Snider, 31st Virginia) June 23, through the day some of the boys captured runaway Virginia negroes.
- (War is the Place, L. T. C. Lovelace, 4th Georgia) 23 June; near Greencastle, PA. Several of our Brigade have brought in several runaway negroes since I have been writing, they belong to a man near Guineas Station, the boys played off on them and caught the bucks.