THE MASSACHUSETTS ASSOCIATION OF HEALTH PLANS on Monday urged the Department of Public Health to reconsider its conditional support for a proposed expansion at Boston Children’s Hospital.

Lora Pellegrini, the president and CEO of the group that represents 17 health plans, wrote Monday to Public Health Commissioner Monica Bharel, expressing concerns over the “potential shift in inpatient volume from lower cost providers” if the hospital is allowed to pursue its expansion. Such a shift, combined with higher reimbursement rates at Children’s, “could significantly increase health care spending in the state,” Pellegrini wrote.

The letter echoes a report issued Tuesday by the Health Policy Commission, which found the expansion could increase health care spending in Massachusetts by $8.5 to $18.1 million a year for commercial payers. Children’s officials have disputed the commission’s findings.

The Department of Public Health last week recommended approval of the $1 billion project, with conditions aimed at preventing increased spending. The recommendation will be presented to the Public Health Council on Oct. 20.

The conditions include requirements that the hospital “not cover its approved final incremental operating costs by passing on the costs” to payers and patients, maintain its commitment to serving Medicaid patients, and report related data annually to the DPH. A DPH spokesman said the recommendations contain “strong remedies” if the project does drive a spending increase, and that the proposal “includes many positive aspects to improve care for the children and families the hospital serves.”