The trade body polled 483 landlords and found 37% of respondents currently have tenants in arrears.
Over the last six months 44% of landlords have experienced rental arrears.
Half of those polled attempted to recoup lost earnings through court proceedings, with some landlords having to wait over three months before their case was heard.
David Salusbury, chairman of the NLA, says: “Paying the rent has to be right at the top of tenants’ priorities as even one month’s arrears, in this climate, could be the straw which breaks the camel’s back.
“The mortgage has to be paid and the vast majority of landlords do everything in their power to make sure this happens.”
But he adds: “It is important to remember that only about 35% of rental properties are secured on existing buy-to-let mortgage finance.
“Contrary to recent reports, most landlords are not expecting to be repossessed and lose their asset.”