Rating service Standard & Poor’s said today that it would lower the credit ratings of all Illinois utilities, “perhaps precipitiously,” if the state Senate passes a rate-rollback bill. A committee passed the measure Thursday on an 11-1 vote.

Exelon of Chicago owns the biggest Illinois utility, Commonwealth Edison. Ameren of St. Louis owns the other three,  Illinois Power, Central Illinois Public Service and Central Illinois Light. S&P currently assigns each a BBB- rating, the lowest investment-grade category. In a bulletin issued today, the rating service says:

If the (rate rollback) bill is successful in moving to the House, we would lower the ratings on all four Illlinois utilities, perhaps precipitously, depending on the circumstances. The severity of the downgrades (possibly to the ‘B’ category in some cases) will ultimately depend on the likelihood that relevant parties will negotiate a compromise before the bill passes in the House and is signed into law.

Another  ratings service, Moody’s, has already dropped the  Ameren subsidiaries to  junk-bond status. As reported in a previous post, Ameren is already suffering  adverse financial consequences, and says a rate rollback could eventually lead to insolvency.