Obamacare enrollees get to choose from fewer doctors and hospitals than typical health insurance plans, according to a new study.

Plans offered on Obamacare insurance exchanges offer 34 percent fewer providers than the average plan offered outside the exchanges, an analysis released Wednesday by the research firm Avalere Health found.

The analysis provides new ammunition for GOP attacks that the law doesn't guarantee access to patients' doctors.

Specifically, exchange networks offer 42 percent fewer oncology and heart specialists, 32 percent fewer mental health and primary care providers and 24 percent fewer hospitals, Avalere said.

"Patients should evaluate a plan's provider network when picking insurance on the exchange," said Elizabeth Carpenter, vice president at Avalere.

The data is the latest evidence pointing to narrow provider networks for Obamacare enrollees as insurers look to ways to contain costs. Another study funded by the Robert Wood Johnson Foundation discovered that four in 10 mid-grade "silver" plans on exchanges had narrow networks where fewer than 25 percent of doctors in the area are covered.

Avalere said it looked at the plans in five states: Florida, North Carolina, Texas, Georgia and California.