COLORADO SPRINGS — The leaders of the conservative Koch network on Saturday blasted the latest health plan alternative drafted by the Republican-led U.S. Senate, saying it doesn’t go far enough to dismantle President Obama’s health-care law.

“This Senate bill needs to get better,” said Tim Phillips, the president of Americans for Prosperity, the network’s political arm. “It has to get better.”

The remarks came as donors who gave at least $100,000 to the network convened for a three-day retreat with top elected officials at the Broadmoor resort in Colorado Springs.

The objections only further complicates the Republican effort in Washington to repeal the Affordable Care Act, positioning the powerful organization led by Charles and David Koch as one of the most prominent critics.

One of the lawmaker’s on the fence about the bill is Colorado’s U.S. Sen. Cory Gardner, who is attending the conference. Gardner campaigned on the promise of repealing the law, also known as Obamacare, and his support may be necessary for Senate passage.

The Koch network, led by Americans for Prosperity, plans to hold Republican lawmakers to their word as it works behind-the-scenes to shape the final bill that goes to President Donald Trump.

“We want to remind them that this was a promise made to repeal Obamacare during four consecutive national elections, beginning in 2010 and that the vast majority of the members have pledged that,” said Phillips, whose organization includes a prominent chapter in Colorado.

The Koch forces are particularly concerned that the bill isn’t conservative enough and it doesn’t do more to shrink the size of Medicaid, the government program that provides health care coverage to low-income adults, children and disabled people.

In an interview with reporters, Phillips said the Senate bill represents only a “slight nip and tuck.” But Gardner has expressed concerns the bill curtails Medicaid’s expansion moves too fast. He was not available for an interview at the event.

Under the health care law, Colorado expanded the Medicaid program and cut the number of uninsured residents from 15.8 percent in 2011 to 6.7 percent in 2015.

Charles Koch and Vice President Mike Pence discussed healthcare Friday in Colorado Springs when the two held an unannounced meeting after the former Indiana governor spoke at Focus on the Family.

Pence is considered one of the Koch network’s key allies in the White House after giving Trump the cold shoulder in the 2016 presidential campaign.

“On healthcare, we’ve had productive discussions with them. We are trying to get to a place that in our view is the right place to be,” Phillips said.

So far, the Koch network leaders are optimistic about the progress being made by the Trump administration, mentioning the appointment of Colorado’s Neil Gorsuch to the U.S. Supreme Court as one of the top accomplishments.

Charles Koch, addressing the 400-plus donors at the event, touted the progress the organization is making, particularly since the 2016 election.

“When I look at where we are — at the size and effectiveness of this network — I’m blown away,” he said. “I’m more optimistic now than ever.”