Moody’s Investors Service slashed BP plc’s senior unsecured issuer and long-term debt securities ratings Friday, marking the second downgrade in a month, CNNMoney.com reported.

Citing the worsening impact of the oil spill, Moody’s cut BP’s long-term rating by three notches, to Aa2 from A2, and said there may be further downgrades as its continues its review.

“Moody’s update assessment is that the spill will have a sustained negative impact on the group’s free cash flow generation and overall financial profile for a number of years,” the rating agency said in a statement.

Also on Friday, Moody’s downgraded the senior unsecured issuer rating of BP Finance by three notches to A3 from Aa3. BP Corporation North American’s senior unsecured issuer rating was cut by four notches to Baa1 from Aa3.

It’s not the first time BP has been downgraded since the oil spill disaster began on April 20. That was the date the Deepwater Horizon offshore rig BP leased from Transocean exploded and sank, killing 11 workers.

On June 3, Moody’s and Fitch Ratings both announced downgrades of the oil giant. Since then, Fitch announced a second downgrade.

BP owns 65 percent of the well that is spilling an estimated 60,000 barrels per day into the Gulf of Mexico. By Thursday’s close, BP’s stock had plunged 47 percent since the accident occurred.