More than 200 family members of some of those who died in the disaster in Smolensk, western Russia, have signed the letter addressed to the Polish authorities and Catholic clergy.
The Law and Justice (PiS) party, which came to power last year, has reopened a probe into the 10 April 2010 plane crash in western Russia, which saw the death of 96 people, including then-President Lech Kaczyński.
Some PiS politicians have claimed the presidential plane was brought down by an explosion, and have challenged a report under Poland’s previous government which concluded the crash was an accident.
According to media reports, the bodies of victims will now be tested for traces of explosives.
PiS leader Jarosław Kaczyński has said his twin brother Lech Kaczyński’s body would be among the first, if not the first to be exhumed.
The letter signed by some of the victims’ families said: “Six years after those terrible days we stand alone and helpless in the face of a ruthless and cruel act: our loved ones are to be taken out of their graves...
“We, the families, have for months unsuccessfully expressed our objection to the announcement of this incomprehensible and unjustified venture.”
Poland’s National Prosecutor's Office announced in June that the bodies of the crash victims were to be exhumed and has recently informed the families in writing.
According to the prosecutor's office, the exhumations will enable new autopsies as earlier reports by Russian experts had “many irregularities”.
The Polish authorities have said exhumations can be carried out without families' consent.
In 2014 the Macierewicz commission, a group of parliamentarians mainly from the then-opposition PiS party, concluded the Polish presidential plane was brought down by an explosion.
This was in stark contrast to earlier official Polish and Russian military reports on the causes of the tragedy, which happened in dense fog on approach to a military airfield lacking ground identification radar.
The Polish report cited a catalogue of errors on the Polish side, while also pointing to errors made by Russian staff at the control tower of Smolensk Military Airport.
The Russian report placed all the blame on the Poles. (vb/pk)