This study aims to specify to what extent the variation introduced in the Estonian object-marking system by Russian-dominant Estonian L2 speakers is spreading to the native usage of Estonian. 669 secondary school students completed a written production task and a grammaticality judgment
task on object marking. The results indicate that the object-marking variation is contact-induced and that the group of fluent bilinguals acts as a bridge for impositional innovations to enter and to be accepted by native speakers. The findings also suggest that multiple causal forces influence
the diffusion of innovations. While any single causal factor may drive diffusion if it is strong enough, the process is greatly facilitated when different causal factors contribute to the same direction. In this case, fairly weak contact is sufficient to induce diffusion.