It has also increased the minimum age for a buy-to-let mortgage from 18 to 25 and raised the minimum income from £15,000 a year to £20,000.
The lender says it is about narrowing the area of the market it wants to lend to.
A spokesman for Platform, says: “Platform is committed to supporting brokers in the buy-to-let market as it is with the mainstream market.
“We have a wealth of experience and expertise in buy-to-let lending and we’re very clear about the area of the market that we want to focus on. This is reflected in our criteria.
The changes to interest-only follow the Royal Bank of Scotland and Coventry Building Society stopping interest-only for first-time buyers, Lloyds Banking Group capping deals at £500,000 and Northern Rock capping mortgages at 75% LTV.