More than half of buy-to-let investors with up to three mortgages have also found it harder to get finance in recent months, the research showed.
Borrowers with four or more mortgaged properties are classified as portfolio landlords under the PRA changes and must adhere to requirements, such as providing a forward-looking business plan.
Around half of landlords aware of the PRA changes believe the process of gaining a mortgage will be slower, as a result of the new rules.
Many buy-to-let investors with 11 or more properties fear the range of mortgage products available to them is set to be reduced.
And more than a quarter worry their mortgage application will be rejected.
Jeff Knight, marketing director at Foundation Home Loans (pictured), said: “Whether these figures are to do with a natural period of adjustment or has become the new norm remains to be seen.
“Nonetheless, in order to make this as smooth a transition as possible, brokers and lenders must work together to ensure things do not become unnecessarily challenging.
“Our research last year proved that, at the end of the day, brokers and landlords are after pragmatic and straight forward processes.
“Considering the significant take-up from this group, we devised a proposition to make application as simple as possible – for example, with no need for evidence of a business plan.”