Germany's GDP Trade Union of Police warned Friday that federal police units responsible for Germany's 3,621 kilometers (2,250 miles) of national borders were overstretched and more trained recruits were urgently needed.

"For a period of perhaps three weeks, we can handle it, but for longer there is not sufficient personnel," said GDP Deputy Chairman Jörg Radek.

Should Austria implement its decision made earlier this week to cap its intake of refugees at 37,000 and flag the rest through to Germany then this would result in "enormous problems" for German police, Radek warned.

On Thursday, Interior Minister Thomas de Maiziere told MDR public radio that identity checks at border crossings since September could be extended indefinitely.

From Brussels, the European Commission responded that any German request to extend checks beyond May would require complex approvals under Article 26 of the EU's Schengen "open borders" policy launched in 1985.

Overtime accumulating

Radek told the daily "Osnabrücker Zeitung" that since September 13, when Germany reintroduced checks, mainly along the border with Austria, some 2,000 officers had accumulated 2 million hours in overtime.

Two million hours of overtime, says Radek

That equates to 1,100 extra officers, he added - on top of 33,000 federal police officers already assigned to tasks such as patrolling German airports, railway stations, trains, guarding federal facilities and coastal waters, tackling organized crime, and providing crowd control during weekend football matches.

Radek said an Interior Ministry plan to create 3,000 new positions over the next three years would not help the federal police struggling to cope with the current refugee crisis.

"That will help us in three years' time, but right now we can't deploy these people," he said.

Ministry rejects complaint

A spokeswoman for the Interior Ministry on Friday rejected the union's complaint, saying that extending border controls was "definitely feasible," adding that Chancellor Angela Merkel's coalition government was doing everything possible to strengthen the federal police.

Formal training at federal police academies lasts between two-and-half and three years and includes short work experience placements at police stations, management and judicial topics.

Germany's nine-nation border includes 784 kilometers shared with Austria, 646 kilometers shared with the Czech Republic, and 451 kilometers with France.

Under Paragraph 30 of Germany's constitution, policing is the responsibility of Germany's 16 regional states or Länder, unless otherwise specified. Special legislation, however, puts border control under the prevue of the federal government.

Migrants wait at Passau, on Germany's border with Austria

The creation of the European Union's Schengen policy in 1985 was followed in 2005 by a reform and renaming of Germany's federal police known since then as the Bundespolizei.

Passport controls were largely reduced to spot checks inside German territory as part of the EU's "open borders" policy.

Two other GdP executives, Clemens Murr and Jürgen Herdes, said crowd control squads - staffed jointly by officers from the Bundespolizei and the Länder - were now overloaded with tasks.

On paper they amounted to 15,900, but staffing gaps were all too apparent because some were away on training, and others had been assigned to other tasks or had called back to their regions to support local operations, Herdes said.

Open borders essential, warns industry

On Thursday, Germany business and trade union leaders warned that a reintroduction of intense border controls in Europe would cripple "just-in-time" cross-border industrial production and logistics.

Germany Chambers of Industry and Commerce head Martin Wansleben told the "Rheinische Post" newspaper that tailbacks and extra bureaucracy would cost German industry tens of billions of euros extra annually.

"Europe needs the free border and movement in goods," Wansleben said, adding that constraints at borders or even closures would result in "unimaginable" impacts.

The head of Germany's DGB trade union federation, Reiner Hoffmann, warned EU nations not to respond to the refugee crisis with self-imposed isolation.

"The open inner-borders [of the EU] are the arteries of the European economy," he told the business daily "Handelsblatt." "They must not be jammed."

Europe's economy was highly integrated and waits of five, seven or nine hours at an inner-EU border would be "poison," Hoffmann warned.

Radek's GdP police trade union belongs to the DGB umbrella federation.