Activists hold signs during a Stop 'Trumpcare' rally in front of the Capitol in Washington, DC.

A new poll shows strong public opposition to the idea of making changes to Obamacare with new tax legislation, as advocates released a series of ads aimed at convincing a group of House Republicans to oppose a bill that would repeal one that health law's major rules.

The CBS News poll found that 68 percent of Americans said that any tax legislation should not include changes to the Affordable Care Act, as Obamacare is formally known.

Just 21 percent of respondents said such changes should be included in a tax bill.

Opposition to tinkering with the ACA as part of a tax bill was broadly bipartisan. A total of 62 percent of Republican respondents oppose that idea, while 72 percent of Democrats object to it.

The question comes as Congress is considering a Republican-sponsored Senate tax bill that would repeal Obamacare's individual mandate, which requires most Americans to have health coverage or pay a fine.

A House version of the tax bill sponsored by the GOP did not call for repeal of the mandate.

But the final version of the legislation to be voted on by Congress is widely expected to include such a repeal after a conference committee made up of Senate and House members resolves differences between the two bills.

All Democratic members of both chambers of Congress are expected to oppose the tax bill if it includes mandate repeal, but Republicans have enough members to pass it on their own.

On Thursday, the Obamacare advocacy group Save My Care announced an ad campaign targeting 13 GOP House members, asking their contituents to call their office and ask them to vote against the tax bill if it includes the mandate repeal.

The 13 House members were among 20 Republicans in that chamber who earlier this year had voted against a bill that would have repealed and replaced much of Obamacare.

The ads note that the Congressional Budget Office has estimated that repealing the mandate will lead to 13 million more people lacking health insurance, and will add an extra 10 percent to the price hikes of individual insurance plans.