The monthly remuneration of such employees would be determined by "reducing pension from his last pay drawn", it said.
The board has also laid down some conditions for re- engagement.
Retired employees being re-appointed should not have been covered under voluntary retirement schemes such as the Safety Related Retirement Scheme or Liberalised Active Retirement Scheme for Guaranteed Employment for Safety Staff, the letter stated.
"While re-engagement of such staff, medical fitness of the appropriate category should be obtained from the designated authorities as per existing practices," it said.
The Northern Railways has already released a notification inviting retired railway employees to apply for 4,500 vacant positions in various departments.
The board's letter also said suitability or competence of the staff should be adjudged before the re-engagement and their safety record as well as other operational requirements adequately addressed.
The offer for re-engagement, the board said, stands till September 14, 2018, and they have to be discharged once selected candidates join from the Railway Recruitment Board.
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(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)