Top Energy and Commerce Democrats have put BP CEO Tony Hayward on notice that the panel’s probe has raised “serious questions about the decisions made by BP” in the weeks prior to the Deepwater Horizon explosion, which prompted the worst offshore oil spill in U.S. history.

Chairman Henry Waxman (D-Calif.) and Subcommittee on Oversight and Investigations Chairman Bart Stupak (D-Mich.) told Hayward in a letter Monday that he should be prepared to field questions about numerous decisions that BP made prior to the April 20 explosion that “appear to violate industry guidelines and were made despite warnings from BP’s own personnel and its contractors.” Hayward is scheduled to testify before Stupak’s panel Thursday.

In the 14-page missive, Waxman and Stupak cited the fact that BP’s drilling engineer called the well in the Gulf of Mexico a “nightmare” five days before it exploded, noting that it was behind schedule and suggesting that the company cut corners on safety to avoid losing money.

“In spite of the well’s difficulties, BP appears to have made multiple decisions for economic reasons that increased the danger of a catastrophic well failure,” the lawmakers wrote. “It appears that BP repeatedly chose risky procedures in order to reduce costs and save time and made minimal efforts to contain the added risk.”

The lawmakers told Hayward he should be ready to answer questions about five specific engineering decisions that the company made regarding the well. Among those was the installation of a full string of “casing” into the well the day before the explosion, forgoing a “tieback” that would have cost an extra $7 million to $10 million and would have taken extra time, but would have been safer.

“A BP plan review prepared in mid-April recommended against the full string of casing because it would create ‘an open annulus to the wellhead’ and make the seal assembly at the wellhead the ‘only barrier’ to gas flow if the cement job failed,” the lawmakers wrote.