Four Republican senators are demanding changes to a GOP proposal to repeal and replace Obamacare, and warned just hours after the bill was released that they "are not ready to vote" on the proposal until it is altered.

It's enough to sink the bill because Republicans can only afford to lose two Republicans in order to pass the measure with a simple majority. Republicans have a narrow 52-48 majority in the Senate.

Sens. Ted Cruz of Texas, Ron Johnson of Wisconsin, Mike Lee of Utah and Rand Paul of Kentucky issued a joint statement announcing they do not support the plan "but are open to negotiation," and discussion before it reaches the floor for debate next week.

Here is the statement:

Currently, for a variety of reasons, we are not ready to vote for this bill, but we are open to negotiation and obtaining more information before it is brought to the floor. There are provisions in this draft that represent an improvement to our current health care system, but it does not appear this draft as written will accomplish the most important promise that we made to Americans: to repeal Obamacare and lower their health care costs.

Paul issued an individual statement arguing that the bill fails to repeal the current healthcare law which the GOP promised voters it would do.

"The current bill does not repeal Obamacare." Paul said. "It does not keep our promises to the American people. I will oppose it coming to the floor in its current form, but I remain open to negotiations."