The aide who is familiar with the plan did not provide details of the changes that are in the works for the legislation, which was unveiled last week and immediately criticized by both conservatives and moderates Republicans.

A likely change would be to add a provision to encourage people, mainly those who are young and healthy, to enroll in insurance plans, the Politico website reported.

A spokesman for Senate Majority Leader Mitch McConnell would not comment on whether votes on whatever bill is finally crafted would be held in the full Senate on Thursday, as originally anticipated.

At least four conservative Republicans have expressed opposition to the draft legislation, saying it does not go far enough in repealing former President Barack Obama’s healthcare law known as Obamacare.

Meanwhile, some moderate Republicans have either withheld judgment or expressed doubts about replacing Obamacare with legislation that is similar to a healthcare measure narrowly passed by the House of Representatives last month.

That measure initially was supported by President Donald Trump, who later was reported to have described it as “mean.”

One moderate Republican, Susan Collins, said on ABC’s “This Week” program on Sunday that she had “very serious concerns” about the bill floated last week. She also expressed doubts that legislation would clear the Senate this week.

Moderates are worried their party’s approach to healthcare would kick too many people off their insurance plans after Obamacare expanded coverage to millions of Americans since it was enacted seven years ago.

A provision ending federal funding of Planned Parenthood, the women’s healthcare provider, for one year has also caused concerns among moderate Republicans.

Conservatives have been calling for an end to federal funding of Planned Parenthood because it performs abortions, even though they are not performed with taxpayer dollars.