TSB is increasing its buy-to-let interest coverage ratio from 125 per cent to 145 per cent.
For loans up to 65 per cent LTV, TSB will charge 145 per cent of five per cent, or pay rate, whichever is highest.
For mortgages from 65.1 to 75 per cent LTV, TSB will require 145 per cent of 5.5 per cent or pay rate.
The changes take place from Thursday.
Any applications before 8pm on Wednesday will not be affected.
The change will also apply to residential mortgage affordability if the borrower also has a buy-to-let loan.
TSB intermediary director Roland McCormack says: “Today’s change will bring TSB in-line with other lenders in the market. We will continue to work with brokers, through our award-winning service, to best guide landlords through this change.”