“Apart from this, for reasons of migration and security policy, it would be too early to end the temporary internal border checks along the German-Austrian land border already on 11 May 2020. The decline in the number of illegal entries at the German- Austrian land border must not obscure the highly fragile situation at the Turkish- Greek border and the ongoing considerable potential for illegal migration along the Balkan route. On the basis of Articles 25 to 27 of the Schengen Borders Code, I have therefore ordered the temporary reintroduction of internal border control at the German-Austrian land border for a six-month period beginning 12 May 2020.”
Letter from Horst Seehofer to EU (pdf)
See: Temporary Reintroduction of Border Control (EC, link)