The average premium for a basic Medicare Part D prescription drug plan will remain stable next year at an estimated $32.50 per month, according to the federal government.

The Centers for Medicare and Medicaid Services said Wednesday that the flat projection comes as Part D plan costs grew by nearly 11 percent in 2014, driven by high prices for specialty drugs.

The reason premiums will be the same is that enrollee spending is low, growing 1.3 percent over the last five years, the agency said.

That low spending rate has kept the average Part D monthly premium for a basic plan between $30-$32 from 2011-15, the agency added.

The cost of premiums has become the latest battleground in healthcare. Earlier this year, opponents of Obamacare seized on projected premium increases for some Obamacare health plans of up to 70 percent.

However, supporters have said that on average the premium increases will be more modest and that plans still have to finalize their rates.

For instance, California's Obamacare insurance exchange said Monday that plans on average would be 4 percent more expensive next year, slightly lower than last year's 4.2 percent increase.