One of the main contenders to take over from Angela Merkel as the leader of the Christian Democrats has triggered a heated row after he suggested Germany should reconsider its constitutional guarantee to asylum.

Friedrich Merz said Germany should be prepared to debate whether the basic right to asylum could continue if the country was in favour of a standardised European immigration and refugee policy.

Germany is the only country in the world with an individual right to asylum written into its constitution. The law, drafted in reaction to the Nazi dictatorship and the Holocaust, is considered sacrosanct by many.

“I have long thought we must be prepared to openly discuss this constitutional right to asylum,” Merz said in the town of Seebach in the eastern state of Thuringia. He said that Germany needed a considerable public debate over whether the right to asylum should be softened with a “legal caveat”, suggesting that he considered the current conditions too generous.

He received a barrage of criticism from other politicians as well as pro-asylum organisations and charities working with refugees. Some accused him of forgetting the crimes of the Third Reich.

Merz made his remarks at the third in a series of hustings events at which the three main candidates hoping to succeed Merkel have been presenting themselves to the party. The hustings have served to underline the extent to which immigration continues to touch a nerve in the CDU and to dominate political debate in Germany three years after Merkel allowed more than a million migrants into the country. The topic is likely to continue to hover over the leadership battle, which is due to be decided on at a CDU party conference at the start of next month.

Merz has pledged to win back at least half the voters the CDU has lost to the rightwing populist party Alternative für Deutschland, many of whom were disgruntled over Merkel’s immigration policy.

He later said he had been misunderstood, arguing in a statement that he had not called into question the constitutional right to asylum, but was trying to emphasise how “we can only solve the problems of immigration and asylum in the European context”.

But some accused him of deliberately sending out a negative message about the asylum law in order to trigger a debate about its future.

Merz drew controversy earlier this week when he stressed his middle-class credentials at the same time as admitting that he earned a million euros a year and owned two private jets. In the hustings, the businessman also questioned whether Germany should be signing up to the UN’s planned migration pact. He said it needed to be clarified that the terms of the pact would not encourage asylum seekers by creating new reasons for them to come to Germany.

He questioned the validity of the pact’s pledge to view climate change as a reason to claim political persecution, calling on an “appropriate” explanation of the deal.

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Jens Spahn, the current health minister, who is considered the underdog candidate in the battle for the CDU leadership, has also urged the party to have more debate about the pact, amid concerns that Merkel has already effectively waved it through.

Merz also indirectly criticised Merkel for presenting the pact to the Bundestag more or less as a fait accompli. “These are things that we in Germany cannot accept via the back door,” he said to applause.

Annegret Kramp-Karrenbauer, secretary general of the CDU and the other candidate running for the leadership post, criticised the non-binding principles contained in the UN asylum pact. “In future we must have a better idea of what is questionable and we must start debating it far earlier,” she told delegates.

But she said that any attempt to get rid of the right to asylum or even to restrict it would go against “the essence of the CDU and the legacy of [former chancellor] Helmut Kohl”. She tweeted: “That it the legacy I am indebted to … “[It is] the difference between us and the AfD.”

The right to asylum was embedded in Germany’s constitution in 1949 as an attempt to go some way to make amends for the dictatorship of Adolf Hitler, under which many victims of Nazi persecution were murdered after being unable to find refuge in other countries.

The UN migration pact, which numerous countries have already vehemently opposed, is due to be adopted at a conference in Marrakech on 10 and 11 December.