The Constitutional Democratic Party of Japan (CDP), the largest opposition party in the Upper House, voted?against a package of bills on the imperial family — in contrast with the position of the Centrist Reform Alliance (CRA) in the Lower House, clouding the prospect for a merger between the two.

The CDP voted against the bills in an Upper House committee on Thursday. It takes the position that the inclusion of a clause about the male offspring of newly reinstated members of the imperial family becoming heirs to the chrysanthemum throne is akin to a “sneak attack,” and that it should be omitted.

A parliamentary panel’s outline of the bills released last month — which among others, propose reinstating male members of former branches of the imperial family through adoption — made no mention of the clause in question. But a subsequent government draft of the bills said their future male offspring would become heirs to the throne, which caught some parties off guard.