NEW YORK (CNN/Money) - Shares of Martha Stewart Living Omnimedia tumbled further Wednesday after congressional investigators said they were expanding their probe of Martha Stewart's sale of ImClone Systems stock late last year.

Shares of the company sank nearly 11 percent in late afternoon trading Wednesday. Stewart is chairwoman and CEO of Martha Stewart Omnimedia (MSO: down $0.73 to $7.44, Research, Estimates), whose stock has dropped more than 60 percent from a 52-week high of $20.93

Congressional committees investigating Stewart's sale of Imclone stock asked the home style guru for more information Tuesday to clear up discrepancies regarding a pre-existing pact with her broker, Peter Bacanovic, and to find out whether one actually existed.

Stewart is being investigated as to whether she benefited from inside information when she sold nearly 4,000 shares of ImClone a day before the Food and Drug Administration refused to review the biotech company's application for its cancer drug, Erbitux, last December.

Stewart, a friend of former ImClone CEO Sam Waksal, has repeatedly said she did nothing wrong and that she had a verbal agreement with Bacanovic, who was her broker at Merrill Lynch, to sell the ImClone (IMCL: down $0.44 to $6.50, Research, Estimates) shares if the price dipped below $60. However, congressional investigators have yet to find written evidence of that pact.

The House Energy and Commerce Committee said Tuesday that the domestic diva is refusing to speak to them, while Stewart's attorney maintains that investigators have not responded to his request to delay an interview.

Martha highlights       Congress wants more Martha documents Investor sues Martha Scandal to hit Martha Stewart profit Congress expands ImClone probe Martha's broker sends records

The investigation into Stewart's sale of ImClone stock in December brought more twists this week. Douglas Faneuil, Bacanovic's assistant, is disputing her explanation for selling the stock, claiming that he called Stewart and urged her to sell because Waksal and members of his family were dumping their ImClone shares, a person familiar with the situation told CNN/Money. But Stewart's assistant, Ann Armstrong, says in a sworn affidavit that it was Bacanovic who actually called Stewart, not Faneuil.

Congressional investigators have yet to find any phone records showing that either called, House Energy and Commerce Committee spokesman Ken Johnson said.