Wealthy Americans who have offshore bank accounts may be sweating more than usual this summer, according to Investment News.

If they have not done so already, offshore account holders have until 23 September to take advantage of the Internal Revenue Service's voluntary disclosure programme and report income in those accounts.

Account holders who do come forward "are more likely to avoid criminal prosecution than those who do not," according to an IRS statement.

Wealth managers and tax lawyers say that they are telling their clients to take the IRS at its word.

To that point, the IRS is vowing to crack down hard on those who don't participate in the programme and get caught. IRS agents have been ordered to pursue "both civil and criminal avenues" and maximum penalties for offshore tax evaders, according to IRS commissioner Doug Shulman.