WASHINGTON - Two Republicans in the U.S. Senate said on Wednesday they will not vote to confirm billionaire philanthropist Betsy DeVos as the next secretary of education, increasing the possibility that the charter-schools advocate will be rejected by the Senate.

Democrats, who have been uniformly opposed to DeVos and are expected to vote against her as a block, only need to bring three Republicans to their side to stop the nomination. She would then be only the 10th Cabinet nominee in U.S. history rejected by Congress.

Soon after Sen. Susan Collins, a Republican from Maine, and Sen. Lisa Murkowski, a Republican from Alaska, said they would not vote for DeVos, the White House said it is confident that she will ultimately be approved.