New Delhi, Sep 6 - Congress and BJP today sharpened their attack on each other on the coal block allocation giving a clear indication that the controversy over the issue is going to further escalate in coming days even after the Monsoon session of Parliament concludes tomorrow. Stepping up the attack on the government and Congress, MPs of BJP-led NDA will hold a dharna in Parliament House tomorrow, the last day of Monsoon session, to protest against the refusal to cancel the licenses of coal blocks.