OMOA president Prasanta Kumar Mohanty and secretary Dillip Kumar Das in a statement threatened to launch strike from May 1 over the issue.
The OMOA district unit has challenged the order issued by the District Collector claiming that it has violated the directives of the Chief Secretary and Principal Secretary, Department of Revenue and Disaster Management.
On April 25, the district collector had shortlisted 135 employees in district-level clerical cadre for transfer. The OMOA delegation had met district collector P Patil over the issue.
"We have requested modification which has been turned down by the district collector," Mohanty said.
Meanwhile, the district collector has gone on a long leave since Monday.