ATLANTA AP-Delta Air Lines pilots have been granted permits to picket at Northwest Airlines hub airports amid a dispute over seniority between the two airlines’ unions that so far has held up a combination of the carriers, according to a memo Tuesday.

The permits grant Delta’s pilots permission to picket at the Minneapolis and Detroit airports, which are considered Northwest crew bases, from Thursday to April 24, a person familiar with the situation said on condition of anonymity because of the sensitivity of the issue.