Senators Michael Bennet (D-Colorado) and Cory Gardner (R-Colorado) voted along party lines Tuesday in a motion to proceed with legislation aimed at repealing all or parts of the Affordable Care Act.

Sen. John McCain (R-Arizona) returned to the U.S. Capitol on Tuesday after surgery and a brain cancer diagnosis to cast a pivotal “aye” vote to advance the legislation.

Senators Susan Collins of Maine and Lisa Murkowski of Alaska, both Republicans, voted no – forcing Vice President Mike Pence to cast the tie-breaking vote.

It was still unclear on Tuesday what will be in the Senate legislation and whether Republicans will ultimately have enough votes to pass it.

In a statement, Gardner said while he voted to proceed, he wants to make some amendments.

“I voted to allow debate today because we can no longer subject Coloradans to a failing healthcare system without working toward solutions, and today’s vote will allow that debate to continue,” the statement reads. “We can now offer amendments in an open setting to fix our nation’s healthcare system and bring relief to the American people.”

Bennet said in a tweet that “it’s shameful that @SenateGOP just voted to take up unknown legislation that could harm millions of Coloradans and Americans.”

This vote was the first step in the path to repealing the health care law. Now that the bill has been brought to the floor, senators are expected to debate various options for repeal.

USA TODAY contributed to this report.