On Friday, a court ruled that Australian Deputy Prime Minister Barnaby Joyce could not serve in parliament because he had inherited New Zealand citizenship through his father.

Read more: Immigrants strive for US passports out of fear of future

Over the past year, Australia's ban on dual citizen nationals serving in federal parliament has forced several lawmakers to step down in both legislative chambers.

DW takes a look at a few policies that govern dual citizenship across the globe and what they mean for people — politicians or otherwise.

Germany: Exceptions to the rule

Germany only recognizes dual nationality under certain circumstances, such as when it is acquired with permission from authorities or if it comes from another EU country or Switzerland.

Read more: Conflicting loyalties? Germany debates dual citizenship

A politician can, however, maintain dual citizenship and serve in public office. For example, David McAllister, who carries German and British citizenship, served as state premier of Lower Saxony from 2010 to 2013, becoming the first person to do so with dual citizenship.

Naturalization is a different story. In nearly all cases, Germany requires applicants to give up their nationalities before acquiring citizenship.

The Netherlands: 'Depending on the situation...'

The Netherlands allows for dual citizenship, but warns applicants that "depending on the situation, you might have to choose between your Dutch and other nationality," which is the government's way of saying that though the policy is liberal, exceptions will be enforced.

In July, for example, Prime Minister Mark Rutte warned Dutch citizens living in the United Kingdom that they would be stripped of their passports if they were to take on British citizenship to avoid having to leave the country after Brexit.

Read more: Brexit in Germany: 'Citizenship is not a panacea' for Brits

In rare circumstances, a Dutch national may obtain another nationality through birthright, prolonged residence or marriage, except from Norway or Austria, which have treaties with the Netherlands that prevent dual citizenship.

For all the rigorous rules, the Moroccan-Dutch lawmaker Khadja Arib, who serves as the speaker of the House of Representatives, shows that in certain situations not only can you maintain dual citizenship, but you can have a successful career in politics with it, too.

India: Only one

In India, citizens are not allowed to hold dual citizenship. Because of persistent demands from the Indian diaspora, the country created the Overseas Citizenship of India scheme, which provides a multiple entry visa and exemption for foreigner registration requirements while in India for the person's life.

It does not give the holder Indian citizenship nor provide any of the associated rights, including the right to vote, to hold public office or to serve in positions of public service.

Read more: India's caste system: Weakened, but still influential

Another contentious area of nationality concerns Indian citizens born in Goa during Portugal's rule — especially those who received identification documents from Portugal between 1958 and 1961. For India, the "Bill of Identity" provided by Portugal to those who had their births registered in the European country's registrar presents grounds for receiving Portuguese citizenship, which is forbidden by Indian law. Instead, India plans to make one choose which citizenship they wish to keep.

China: Above all

China "does not recognize dual nationality for any Chinese national," according to Article 3 of the country's Nationality Law. Furthermore, the law explains that citizens who acquire another nationality of their "own free will" automatically lose their Chinese passports.

Read more: China's Communist Party enshrines 'Xi Jinping Thought' in constitution

Issues become particularly murky when you're a citizen of Hong Kong, which has special status following the 1997 handover by the UK. According to an addendum meant to clarify Hong Kong citizens' status, it states: "All Hong Kong Chinese compatriots are Chinese nationals, whether or not they are holders" of a British passport.

In January 2016, Foreign Minister Wang Yi said Lee Bo, a controversial bookseller who held Hong Kong and British passports and was forcefully disappeared, was above all a citizen of China. When it comes to China, one is first and foremost a Chinese citizen.

Austria: Integration first

Austria expressly forbids the acquisition of another citizenship, except in rare circumstances. According to the Austrian foreign ministry, you "automatically" lose Austrian citizenship "upon obtaining foreign citizenship."

Likewise, if you join the armed forces of a foreign country or worked for a foreign government and are "adversely affecting the interests and reputation" of Austria, you lose citizenship.

Read more: Dual citizenship in Europe: Which rules apply where?

In some cases, gaining or retaining Austrian citizenship is a question of how famous a person is. For example, Arnold Schwarzenegger was allowed to retain his Austrian nationality upon becoming a US citizen, while German actor Christoph Waltz received Austrian citizenship after being awarded an Oscar for the film "Inglorious Basterds."

Save for a few exceptions, Austria has one of the most difficult processes to obtain citizenship and keep it, requiring one to sign an integration agreement, have a "positive attitude" toward the republic and have lived in the country for a minimum of 10 years.