A little-noticed clause in sweeping changes to Germany’s military service policy has caused uproar after it emerged that the law requires men aged up to 45 to get permission from the armed forces before any significant stay abroad, even in peacetime.

The legislation, which went into effect on 1 January, aims to bolster the military and demands all 18-year-old men fill out a questionnaire to gauge their suitability to serve in the armed forces, but stops short of conscription.

If the “modernised” model fails to pull in enough recruits, parliament will be compelled to discuss the reintroduction of compulsory service, the defence minister, Boris Pistorius, said as the legislation passed the lower house of the Bundestag in December.

The fine print, which went largely under the radar until a media report called attention to it this week, says men aged 17 to 45 would have to apply for authorisation to leave Germany for more than three months.

The clause could potentially affect millions of German citizens embarking on anything from a gap year or study abroad to a new job or sabbatical.

It touched off agitated media coverage in a country where the changes to the military service policy have already led to street protests by school pupils subject to the law’s new requirements.

The defence ministry confirmed the requirement first reported by the Frankfurter Rundschau newspaper.

A ministry spokesperson said the new legislation was designed to establish a framework for conscription if required, making it necessary to know potential conscripts’ whereabouts in case of urgent need.

“According to the wording of the law, males aged 17 and over are obliged to seek prior approval from the relevant Bundeswehr career centre for stays abroad lasting longer than three months,” they said. The law stipulates that obligation ends at the age of 45.

The policy requires the authorisation for permission to be abroad for a lengthy period even outside times of crisis, reviving a decades-old rule. However, the ministry said it remained largely without consequence for the men in question.

“The regulation already applied during the cold war and had no practical relevance; in particular, it is not subject to sanctions,” the spokesperson said.

The ministry did not say how many people had made a request for permission this year.

The spokesperson indicated that approval for periods abroad would be routine as long as conscription was not in force and Germany was not facing a security emergency.

“We will clarify through administrative regulations that authorisation is deemed to have been granted as long as military service is voluntary,” they said, adding: “As military service under current law is based exclusively on voluntary participation, such authorisations must, in principle, be granted.”

The spokesperson said there would be a wide berth for exceptions to the authorisation requirement “partly to avoid unnecessary bureaucracy”.

It remained unclear, however, what procedure men would need to use to gain permission before the eased regulations take effect or how long it would take.

The policy is intended to find enough volunteers to increase the ranks of the military to 460,000, consisting of 260,000 active soldiers and 200,000 reservists, by 2035. The country has 182,000 active soldiers and just under 50,000 reservists.

Compulsory military service was suspended in 2011 under the then chancellor, Angela Merkel.

The German chancellor, Friedrich Merz, wants to create the strongest conventional army in Europe amid the increased threat from Russia, since the Kremlin’s full-scale invasion of Ukraine, and doubts about the US commitment to European security under Donald Trump.

Last year, Germany exempted most defence expenditures from the country’s constitutional “debt brake”. It also earmarked more than €500bn (£436bn) for defence between 2025 and 2029.