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".
More top news
Weather set to improve with plenty of sunshine by Saturday
Tony Davis was the first civilian to reach Pc Palmer after he was stabbed during the Westminster attack.
Defiant Londoners put on a show of solidarity for the victims of the Westminster terror attack at a vigil in their honour.