This August has become the season of Congressional letters, whether to the President on Elizabeth Warren, or to the Speaker on the use of food stamp cuts as offsets to future bills. Today, we have another installment.

Raul Grijalva and Lynn Woolsey, the co-chairs of the Progressive Caucus, have sent a letter directly to Erskine Bowles and Alan Simpson, the co-chairs of the President’s deficit commission. In it, they say in no uncertain terms that cuts to Social Security, including an increase in the retirement age, must be off the table.

We write to express our strong opposition to any potential proposal from your commission that would undermine Social Security by reducing benefits, increasing the retirement age, or privatizing elements of the program.

Social Security runs an annual surplus of $100 billion, and is by law prohibited from incurring any debt that would contribute to the national deficit. Because Social Security is not the cause of our national deficit, attempts to reduce it by cutting benefits would be misguided.

For 75 years, Social Security has been a promise to the American people that if they work hard and pay their share, they will have a financially secure retirement. This promise includes Supplemental Security Income (SSI), survivor benefits and retirement benefits. In communities across this country, Social Security benefits are often the only thing helping families maintain a decent standard of living. We will not allow the commission to reduce Social Security payments, especially during an economic downturn that has wiped out trillions of dollars in net worth around the country.

They close by warning that Congress will have a say in the matter of enacting the recommendations.

While this letter was signed only by Grijalva and Woolsey, a Grijalva spokesman assures me that there will be “plenty of CPC-wide followup” when Congress returns to session in September. The Progressive Caucus has 82 members, 80 in the House and 2 in the Senate. If they stay unified, they represent a formidable challenge to getting any recommendations passed. However, the makeup of the recommendations is key, as they could be put together to garner conservative support, making moderate Democrats the swing voters. One such moderate, North Dakota’s Earl Pomeroy, said yesterday that benefit cuts, including raising the retirement age, were absolutely unacceptable.

UPDATE: DCCC Chair Chris Van Hollen has weighed in as well with some encouraging news:

“The consensus position in the caucus is we can preserve the existing structure of Social Security including the retirement age,” said the Maryland Democrat. “And that is where we are. Obviously, people have, whenever they talk about the issue, there are different ideas. But it was very clear from the statements that we made as the Democratic caucus on the front steps of the Capitol that we believe that we should not be changing the retirement age.”

UPDATE: House members have also this week held hundreds of events across the country, and at all of them, Democrats to a man have rejected raising the retirement age.