More than 100 medical groups sent a joint letter to Congress Wednesday urging lawmakers to fund research on gun violence at the Centers for Disease Control and Prevention.

The Guardian reported the letter requests that Congress “end the dramatic and chilling effect of the current rider language restricting gun violence research and to fund this critical work.”

A 1996 bill prohibits the agency from using funds to “advocate or promote gun control,” which has contributed to the decades-long drought of research into the subject. The amendment has been interpreted as prohibition on all gun violence research at the CDC, though former congressman and author of the bill Jay Dickey has called on lawmakers to end the prohibition.

Medical groups said that the language of the law doesn’t necessarily prohibit research into gun violence as a threat to public health, but the lack of funding for the research causes a “de facto ban,” The Guardian reported.

The 141 organizations that signed the petition represent more than 1 million health professionals in the U.S., according to the newspaper. The groups demand that the funding for the research should be included in funding for the next fiscal year.

President Obama has repeatedly requested the CDC to study gun violence. He ordered the agency to do so after the 2012 Newtown shooting and in 2013 he asked the agency to find ways to prevent gun violence. He also requested $10 million in 2014 and 2015 to fund the research but was blocked by Congress, The Guardian reported.

The groups have cited numerous research questions that the CDC could address, including how to prevent gun suicides and child deaths from gun accidents.

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