Barclays has become the latest lender to impose tougher checks on landlords looking for mortgages.
The bank will require landlords to receive more in rent relative to their mortgage costs from next Thursday.
The bank has increased its minimum rental cover, which is the amount that rental payments exceed mortgage costs, from 135pc to 145pc.
The announcement follows last month's decision by Britain's second-largest lender, Nationwide, to tighten its criteria for buy-to-let landlords.
The Mortgage Works, the building society's specialist buy-to-let arm, announced that it would require landlords to receive 145pc on their mortgage costs in rental payments, an increase from 125pc.
Experts predicted that the decision would provoke a "domino effect", with many other lenders following suit, making it more difficult for thousands of landlords to get a mortgage.
Both decisions follow a consultation announcement from the Bank of England, which has said it will consider forcing lenders to take into account other costs for landlords when deciding whether they can lend them money for property, such as fees and tax.
From next year a new system of taxation will gradually remove landlords' current ability to offset their mortgage interest against their rental income when calculating their tax bill - meaning they effectively pay tax on their turnover, not their profit.
The new tax system is expected to hit higher-rate taxpaying landlords with large mortgages particularly hard, with many expected to become loss-making.
Those whose properties are in areas where rents are low relative to house prices, such as London and the South East, are also more likely to struggle.
The bank said its existing provision to allow people to use their salary to make up any shortfall would still stand.
Earlier this year a new EU law, the Mortgage Credit Directive, was introduced requiring lenders to look more closely at borrowers' income before approving them for a loan.
Experts said the tightening regulation, harsher criteria and tax changes meant the buy-to-let rental market would become a "wealthy person's game", with richer landlords still able to get a mortgage, while more ordinary investors are forced to sell up.
Simon Collins, of broker John Charcol, said: "In London and the South East especially, a lot of people who weren't necessarily rich or wealthy were doing buy-to-let because they didn't understand pensions, and saw property as a safe, tangible asset.
"Let to buy - where homeowners rent out their main home to raise cash to move - was very, very popular, and the people doing it were not wealthy people. Those are the people who will now struggle."
A Barclays spokesman said: "As a responsible lender, Barclays Mortgages wants to ensure that aspiring landlords can continue to meet all their financial commitments and are protected as they look to invest in buy-to-let over the long term.
"Customers will continue to complete a full income and expenditure assessment and we will continue to allow personal disposable income to make up any shortfall in the rental cover calculation."
olivia.rudgard@telegraph.co.uk