WARSAW (Reuters) - Poland’s president Andrzej Duda, an ally of the right-wing government, on Friday vetoed a law that would demote Communist military officers who were responsible for introducing martial law in 1981.

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“I refuse to sign this bill and I am sending it back to parliament to discuss it again,” Duda said in a televised address, describing it as unfair.

The bill would have reduced to the rank of private those generals and military officers who served on the military council which ran Poland during communist times from December 1981 until July 1983, many of who are now deceased.

They would have had no right of appeal.

Duda’s move may be seen as a bid to improve his chances for re-election in 2020. Support for the ruling Law and Justice party (PiS), his ally, fell 12 percentage points over one month in a poll published on Thursday.

“One has to remember that a president who wants to win in the first or second round has to win much more votes than the ruling party in a general election,” Rafal Chwedoruk, a political scientist from Warsaw University, said.

“A recent poll has shown that the vast majority of Poles are against demoting generals. ... The number of PiS voters from villages and small towns accepted the decision on imposing martial law,” Chwedoruk said.

The PiS has made much of its efforts to erase the legacy of four decades of post-war Soviet-dominated communist rule and restore what it considers to be Poland’s true identity - even though some leading PiS figures are former communists.

The law would demote to the rank of private members of the Military Council of National Salvation (WRON), led by the late generals Wojciech Jaruzelski and Czeslaw Kiszczak.

But it would also demote 77-year-old Miroslaw Hermaszewski, Poland’s only astronaut, one of the few WRON members still alive, who was drafted onto the council in 1981 without his knowledge or consent, and discharged from it after two weeks.

Hermaszewski spent almost eight days on board the Soviet Salyut space station in 1978, and is still seen as a national hero, also by PiS voters.