BRUSSELS (Reuters) - The EU’s executive arm, the European Commission, is concerned that reintroducing a different retirement age for men and women in Poland could violate the bloc’s equality rules, according to a letter from Brussels to Warsaw seen by Reuters.

FILE PHOTO: Deputy Prime Minister Mateusz Morawiecki speaks at the Reuters Central & Eastern Europe Investment Summit at his office in Warsaw, Poland May 25, 2017. REUTERS/Kacper Pempel

Poland’s ruling Law and Justice (PiS) party and President Andrzej Duda - who comes from the same political grouping - campaigned on promises to undo a 2012 reform that had been gradually raising and equalising the retirement age at 67.

The government’s change, largely popular among Poles, will take effect from October, reintroducing a retirement age of 65 for men and 60 for women.

“Equal treatment between women and men is a key pillar on which our Union is based,” top EU officials for justice and gender equality, Vera Jourova, and employment and social affairs, Marianne Thyssen, wrote to Poland’s labour minister, Elzbieta Rafalska.

“The Commission has concerns about the changes in the Polish statutory pension system which might be incompatible with EU law.”

Poland’s Deputy Prime Minister Mateusz Morawiecki defended the government’s change, saying women should have the right to retire earlier because they have more responsibilities, including raising children.

“The role of women must be appreciated and therefore the legislators provided for the possibility of an earlier retirement,” Morawiecki told the Catholic Trwam television when asked to comment on the Commission’s letter.

“What we propose reflects not only social expectations but also different roles for women, different roles for men.”

Economists have warned the Polish move will hit growth and public finances, at a time when the PiS has already sharply increased state spending.

Brussels has already raised the issue in its criticism of separate PiS-sponsored legal moves to put courts and judges under more direct government control.

As part of this change - which the rest of the EU as well as democracy watchdogs and Polish opposition parties criticise as undermining the rule of law - male and female judges would be allowed to retire at a different age.

The Commission explained in its letter to Rafalska that, while countries were not obliged to legislate for equal retirement ages immediately, a permanent exemption from the general aim of reaching gender equality on social protection was not possible.

The case is yet another rift between Poland and the EU because the PiS has already clashed with the bloc over democratic principles, migration, and large-scale logging of the primeval Bialowieza forest.