Washington ? Former Enron chairman Kenneth Lay will assert his right against self-incrimination and refuse to answer questions when he appears before Congress under subpoena this week, his spokeswoman said Sunday night.

“Under the instruction of counsel, Mr. Lay will exercise his Fifth Amendment rights at the Tuesday hearing,” Kelly Kimberly said in Houston.

She declined further comment.

Two committees snubbed by Lay a week ago have issued subpoenas compelling him to appear. Some lawmakers had said they expected he would assert his constitutional right against self-incrimination, though his attorney had not previously indicated he would do so.

“We will be respectful but tough,” in questioning Lay, Sen. Byron Dorgan, D-N.D., chairman of a Senate Commerce panel on consumer affairs, had told CNN earlier Sunday.

Lay has been subpoenaed to appear Tuesday before the Senate Commerce Committee and on Thursday at a hearing of the House Financial Services subcommittee on capital markets.

Lawmakers say they have not considered granting immunity from prosecution to Lay or other Enron executives in return for their testimony, because they do not want to interfere with the Justice Department’s criminal investigation of Enron. Congress can compel witnesses to show up but cannot force them to answer potentially incriminating questions without granting them immunity from criminal prosecution.

Lay’s colleague at Enron, former chief executive officer Jeffrey Skilling, did testify last week.

But a number of leaders of Congress’ investigations of the Enron collapse made clear earlier Sunday that they didn’t believe the sworn testimony of Skilling. One suggested Skilling could face accusations of perjury as a result of his testimony.

Lay, who was a friend and political backer of President Bush, has not spoken publicly about the Enron disaster since the company entered bankruptcy in December.

Lay’s wife, Linda, said recently there were some things about Enron’s finances her husband wasn’t told about by other company officials.

After an intense week of hearings, lawmakers say they have strong evidence of illegal activity surrounding the failure of the energy-trading company, which slid into the biggest bankruptcy in U.S. history on Dec. 2.