BERLIN (Reuters) - Germany cannot afford to give in to intimidation and threats of protectionism from U.S. President-elect Donald Trump, and to do so even once would invite repeated bullying, a key conservative ally of Chancellor Angela Merkel said on Tuesday. Trump warned German car companies that he would impose a border tax of 35 percent on vehicles imported to the U.S. market, in a newspaper interview published on Monday. Norbert Roettgen, head of Germany’s foreign affairs committee in parliament, said Germany must stay true to its values. The country is one of the world’s leading exporting nations, getting nearly half its gross domestic product from exports. “The smart thing to do is not to yield to intimidation and threats,” Roettgen told a small group of foreign reporters when asked about German industry’s readiness to stand up to Trump. “If you take this path once, you will become the object of threats and intimidation,” said Roettgen, a leader in Merkel’s Christian Democrats. “And I don’t think that makes sense either for Germany as a whole or for individual companies.” A BMW (BMWG.DE) executive said on Monday the carmaker will stick to its plans to open a Mexican plant in 2019, despite Trump’s warnings of a border tax on the German brand’s vehicles made in Mexico and destined for the United States. “I think it is politically right and economically wise to stick to our principles and our policies, which for Germany is a policy of open and fair trade,” Roettgen said. Merkel told German industry leaders on Monday that she would remain committed to free trade, in an indirect rebuttal to Trump’s comments about border taxes on car imports. Vice Chancellor Sigmar Gabriel responded to Trump’s comment that too many German and too few U.S. automobiles were on the streets of New York by saying the United States “should build better cars.” On Tuesday, Gabriel issued an indirect warning to Trump against stoking nationalism and promoting protectionism: “Nationalism and protectionism are not the recipes for greatness,” Gabriel said in a speech in Berlin. The United States is Germany’s top trading partner. 