A group of Democratic senators is urging the Obama administration to delay a key portion of Obamacare because the results could be “harmful and disruptive.”

In a letter exclusively obtained by The Daily Caller, Senate Democrats pleaded with Health and Human Services secretary Sylvia Matthews Burwell to delay an Obamacare rule change that puts companies with 51 to 100 employees in the costlier “small group” market instead of the “large group” market. The rule change, which will result in higher premiums for many companies, goes into effect in 2016.

The letter was signed by Democratic Sens. Claire McCaskill, Heidi Heitkamp, Chris Coons, Joe Manchin, Joe Donnelly and Jon Tester and independent Sen. Angus King, who caucuses with the Democrats.