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
Rain across much of the remainder of the country
Singer knocks Oasis from their 18-year hold on the top spot as her third album sells more than 800,000 copies in its first week of release
Francois Hollande has urged British MPs to support David Cameron's plan to launch airstrikes against so-called Islamic State in Syria.