The BJP, engaged in a tussle with ally Shiv Sena over power sharing in Maharashtra, may soon have another battle on its hands. In Bihar, Chief Minister Nitish Kumar's Janata Dal United today said it was open to an offer of a cabinet berth in the Narendra Modi government at the Centre. The party, however, insisted that it would stick to its demand of proportional representation, which proved a deal breaker the last time.