While NHS trusts locally make the decisions about staffing levels, the RCN said there is a lack of national oversight about the reduction in staff numbers.
The organisation is calling on ministers to prevent NHS trusts from "continuing with this damaging agenda of cuts" that "impact on patient care".
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Rain will spread eastwards across southern areas tonight. Clear and frosty in the north.
Political leaders will go head-to-head at ITV's studios in MediaCityUK in Salford, ITV has confirmed, as the set for the event is unveiled.
More than 100 people claiming to represent working people across Britain have signed a letter backing Labour in the general election.