ALLENTOWN, Pa.  Though Senator John McCain has promised to not raise taxes, his campaign acknowledged Wednesday that the health plan he outlined this week would have the effect of increasing tax payments for some workers, primarily those with high incomes and expensive health plans.

The campaign cannot yet project how many taxpayers might see their taxes go up, said Douglas Holtz-Eakin, Mr. McCain’s top domestic policy adviser. But Mr. Holtz-Eakin said in an interview that for some, Mr. McCain’s health care tax credits would not be large enough to compensate for his proposal to eliminate the tax breaks afforded to workers with employer-provided health benefits.

On stops in Florida and Pennsylvania this week, Mr. McCain, the presumptive Republican presidential nominee, has emphasized a free-market approach that he said would lower health care costs and make insurance affordable.

To do so he is proposing a major tax change that he hopes will make the insurance marketplace more competitive and less expensive in part by encouraging more people to buy health insurance on their own instead of receiving it from their employers.