BALTIMORE — A first-of-its-kind state law that would have required Wal-Mart Stores Inc. to spend more on employee health care in Maryland is invalid under federal law, a judge ruled yesterday.

The state law would have required non-governmental employers with 10,000 or more workers to spend at least 8% of payroll on health care or pay the difference in taxes. The measure was aimed at Bentonville, Ark.-based Wal-Mart, which has been under attack by critics who say that its inadequate health care offering is forcing some employees to use state-funded plans.

U.S. District Judge Frederick Motz decided that the Maryland Fair Share Health Care Fund Act would have hurt Wal-Mart by requiring it to track and allocate benefits for its Maryland employees in a different way from how it keeps track of employee benefits in other states. Judge Motz wrote that the law “imposes legally cognizable injury upon Wal-Mart.”

Judge Motz cited the federal Employee Retirement Income Security Act, which he said pre-empts “any and all state laws insofar as they may now or hereafter relate to any employee benefit plan.”

“My finding that the act is pre-empted is in accordance with long established Supreme Court law that state laws which impose health or welfare mandates on employers are invalid under ERISA,” Judge Motz wrote in his 32-page opinion.

Wal-Mart’s chief executive, Lee Scott, said the ruling meant businesses would not have to contend with different standards in different states for health coverage.

“The thing that we find encouraging is that there is going to be consistency, that the federal government is going to be the control point on health insurance and these kinds of issues, so that commerce itself, businesses, will be able to have one set of standards that they work against,” Mr. Scott said during an appearance on the Rev. Al Sharpton’s syndicated radio show.

Kevin Enright, a spokesman for the Maryland attorney general’s office, said the state would appeal to the 4th U.S. Circuit Court of Appeals in Richmond, Va.

Mr. Enright said the state disagreed with Judge Motz on several counts, particularly in finding that the law is preempted by ERISA.

“Supreme Court precedent makes it clear that this law does not impermissibly impact health benefit plans,” Mr. Enright said. “Employers may choose to pay the tax or avoid paying the tax in several ways.”