WARSAW (Reuters) - Thousands of Poles dressed in black marched through city streets in Poland on Monday, closing down government offices, restaurants and other businesses in protest against a petition for a total ban on abortion.

The ruling Law and Justice (PiS) party has put forward the proposal - from a group called Ordo Iuris - for debate in parliament. Critics of the new rules say PiS may back them for fear of angering the church in staunchly Roman Catholic Poland.

Poland’s already restrictive laws only allow abortion in the case of rape, incest, a threat to a pregnant woman’s health, or when the baby is likely to be permanently handicapped.

Women and doctors could face prison if convicted of causing what the proposed rules call “death of a conceived child”, and critics say doctors would be discouraged from doing prenatal testing, particularly if that carried the risk of miscarriage.

Protesters chanted: “We want doctors, not missionaries!” and “Jaroslaw, get out!” in front of the central Warsaw offices of PiS leader Jaroslaw Kaczynski.

Some carried posters saying: “A government is not like a pregnancy - it can be terminated.”

The protests and accompanying strikes caused widespread disruption to businesses, traffic and to government offices.

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In Warsaw, demonstrators blocked access to headquarters of PiS, which swept to power a year ago promising to narrow the wealth gap and instill conservative values in public life.

Authorities in the capital said some 25,000 people marched through Castle Square in the city centre, and others held book readings or blood donation drives. Some teachers taught classes wearing black.

“I didn’t go to work today,” said Gabriela, a 41-year-old market researcher from Warsaw.

“They are violating our civic rights, and I wanted to support all the women who may be hurt, who may be denied medical help and forced to have a disabled child... And I am doing it for my daughter.”

So far, public support for PiS has held roughly steady at just below 40 percent, despite criticism from the European Union and the United States that some of the government’s policies have undermined democratic checks and balances.

One poll, however, showed public backing for PiS falling to 29 percent on Monday.

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“Liberal and left-wing communities appear galvanised. One source of that is the abortion law,” Marcin Duma, head of the IBRiS pollster, said.

PiS officials have been quoted in local media saying the party may introduce its own proposal that would allow abortion in the case of rape and incest and a threat to the mother’s health but ban terminations of potentially handicapped babies.

“The right to life, or as some insist, the right to an abortion, is an important moral challenge for our civilisation, our Western civilisation,” Foreign Minister Witold Waszczykowski told RMF FM radio.

“Let them have fun,” he said of the protesters. “They should go ahead if they think there are no bigger problems in Poland.”

In Brussels, about 500 demonstrators dressed in black gathered outside the European Union buildings to show solidarity with the Polish protesters.

“I hope the (Polish) parliament and government will think about half of the citizens as citizens,” Grażyna Plebanek, a Polish writer who has lived in Brussels for 11 years, said.

Official statistics show several hundred legal abortions are conducted in Poland each year. But activists say many women are denied access to the procedure when doctors invoke a legal right to decline to perform it on moral or religious grounds.

Tens of thousands are done illegally, activists say, and many women get abortions over the border in Germany or Slovakia.