Sen. Tom Cotton of Arkansas. AP Sen. Tom Cotton, the influential Arkansas Republican, used Twitter on Thursday morning to express his displeasure with House Republicans' new healthcare legislation and the speed at which it was advancing through Congress.

"House health-care bill can't pass Senate w/o major changes," Cotton tweeted. "To my friends in House: pause, start over. Get it right, don't get it fast."

Numerous senators have expressed misgivings about the Republican replacement plan for the Affordable Care Act, the healthcare law better known as Obamacare. Some, including Sen. Rand Paul, of Kentucky, have criticized the law as not going far enough in its repeal. Others have worries about the future of Medicaid funding. The opposition has health-policy experts wondering whether the law can make it through the upper chamber.

Cotton's state of Arkansas is one of 34 states and the District of Columbia that went ahead with the Affordable Care Act's Medicaid expansion. That has allowed more than 11 million people nationwide to access Medicaid insurance and has become incredibly popular in the states where it has been expanded.

The new GOP bill, the American Health Care Act, would end the funding for Medicaid expansion in 2020 and shift to a per capita system of block grants that many experts say would result in less Medicaid funding for states. Additionally, the law would not allow anyone to be added to the expansion rolls after 2019, slowly decreasing the total number of Americans covered by Medicaid.

Cotton also said he was opposed to the fast track on which the bill was moving through the House. The AHCA was introduced Monday evening by the GOP leadership and is now being reviewed by committees before it goes to the House floor for a vote.

"GOP shouldn't act like Dems did in O'care," Cotton wrote. "No excuse to release bill Mon night, start voting Wed. With no budget estimate!"

Cotton was referring to the fact that the nonpartisan Congressional Budget Office has not released a score for the AHCA. The score gives estimates on the budget impact of the bill and how many Americans' health coverage would be affected.

Cotton is a longtime supporter of President Donald Trump, who has publicly supported the law and attempted to win over conservatives to get the law through Congress.

Despite this, Cotton made his opposition to the bill's existing form known Thursday.

"What matters in long run is better, more affordable health care for Americans, NOT House leaders' arbitrary legislative calendar," Cotton said.

Check out the tweets: