Previously shareholders were restricted to owning no more than 10 percent of the company, according to a Monday filing with the Securities and Exchange Commission.

Thornburg is offering $1 billion in convertible notes -- special bonds that draw interest before converting to common stock. As of late Monday, there was no indication if Thornburg had completed the special stock offering, according to Dow Jones Newswires.

The notes carry an interest rate of 12 percent and mature in 2015. They then would convert at a price as low as 75 cents per share. Shares of Thornburg closed Monday at $1.27.

Last week, Thornburg said it would offer the notes as it faces mounting margin calls and demands for more collateral from its creditors. Raising the capital would help Thornburg avoid margin calls for one year and continue to operate.

As delinquencies and defaults across certain types of mortgages have risen, investors have shied away from purchasing nearly all types of loans in the secondary market.

That lack of a market to sell debt backed by mortgages has caused prices to plummet. As those prices fell, companies like Thornburg have been forced to reduce the value of their holdings, regardless of actual performance. Those declining prices also have lenders making margin calls.

Santa Fe, N.M.-based Thornburg did not immediately return calls seeking comment.