Advocates of strict regulations on banks are already pressuring Congress not to include financial deregulations in must-pass spending bills, renewing early a large-scale effort that last year frustrated banks and their Republican allies in Congress.

In a letter sent Wednesday to members of Congress, 254 outside groups, including many unions and left-leaning non-profits, warned legislators who are beginning work on government funding bills not to include any "riders" rolling back the 2010 Dodd-Frank financial reform law or other new Obama financial regulations.

The letter warned Congress against "using backroom deals to put the public interest at risk and deliver a wish list to narrow Wall Street interests."

At the top of their concerns are GOP efforts to change the structure of the Consumer Financial Protection Bureau, the consumer agency created by the Dodd-Frank law that has wide jurisdiction and independence from Congress.

A new worry this year is that Republicans may try to block a new Obama rule on conflicts of interest in retirement advice, a far-reaching rule planned by the Department of Labor that the GOP has claimed will price out low-income savers.

Among the signatories to the letter were the retirees' group AARP, the union group AFL-CIO and the financial reform advocates Americans for Financial Reform.

Last year, congressional liberals blocked significant changes to Dodd-Frank or other banking rules in the omnibus spending bill that prevented a government shutdown, frustrating bank lobbyists.

The previous year, however, one notable Dodd-Frank rule, pertaining to certain speculative trades by banks, was attached to a spending bill signed by President Obama, despite outraged opposition from congressional Wall Street critics such as Sen. Elizabeth Warren, D-Mass.

Over the course of 2015, Democrats in Congress and the Obama administration warned that they would oppose financial riders in spending bills. Ultimately, they were successful even though at different points of the legislative process such policy changes were include in legislative text.