Meanwhile, Müller's cabinet also had to deal with diplomatic problems with Poland over trade and ethnic minority questions. German-Soviet relations also reached a nadir, as the Soviet government blamed the cabinet for violence between communist demonstrators and the police in Berlin in May 1929. At that point, the bourgeois parties were looking for ways to end the coalition with the SPD. There were attempts to stop the Young Plan via a referendum and the coalition parties disagreed on the issue of unemployment insurance. Müller himself was unable to participate in the political arena for several months due to a life-threatening illness.