Opposition within Germany’s Christian Democratic Union to a UN Global Compact for Migration has grown despite Chancellor Angela Merkel's backing.

There are growing reservations within Angela Merkel's Christian Democratic Union (CDU) about Germany signing onto the United Nations' migration pact.

Health Minister Jens Spahn, who hopes to lead the CDU when Merkel steps down as party leader later this year, has suggested that Germany should not sign the pact and called for further debate on the issue.

Other CDU members have also criticised Germany's participation in the pact, which is set for ratification in December.

Spahn and other members of Germany’s governing coalition of the CDU, Social Democrats and Bavarian Christian Social Union (CSU) who have gone rogue on asylum policy, are apparently taking cues from the country’s neighbours — Poland, the Czech Republic, Austria, and Hungary, who have already pulled out of the pact.

Meanwhile, leading Christian Democrats are hitting back at Spahn’s and others’ idea of not signing the pact, which in part "intends to reduce the risks and vulnerabilities migrants face at different stages of migration," according to the UN.

"To put off signing the migration pact would be a lack of leadership that Germany cannot permit," Norbert Rottgen, who heads the Bundestag's foreign affairs committee, told the daily broadsheet Bild.

He added that the agreement, which is not legally binding, would be an important step by the international community in controlling migration and was therefore in Germany's best interest.

This may not be enough to convince the right-leaning members of Germany’s ruling coalition though. In an interview with the daily newspaper Die Welt, CSU Bundestag deputy Peter Ramsauer, who opposes the pact, said that "throughout the entire document, there's a stance that sees migration as something normal and even desirable”.

The non-legally binding Global Compact for Migration was finalised in July and is set to be adopted by UN member states in December.

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The pact urges countries to take voluntary measures to help improve the conditions in migrants' countries of origin that are frequently cited as the primary motivators of emigration, as well as to help destination countries better assimilate migrants and provide them with sustainable conditions.

Eight countries, including the US, Australia, and Italy, have either already withdrawn or have signaled an intention to withdraw from the pact.

The United States was the first to announce it would not join the pact. It was followed by Hungary, Australia and Austria, Poland, the Czech Republic, Slovakia, and Italy who have signaled they may withdraw as well.