This could be Elizabeth Warren's next thing

It doesn't sound very sexy, but stock buybacks could become the next big issue in Congress - and on the Street.

Some Democratic senators have started pointing to buybacks, in which publicly traded companies repurchase some of their stock from shareholders, as a new rallying point in the populist wing's ongoing battle to bolster bank regulation.

Here's what Sen. Tammy Baldwin (D-Wis.) wrote in a letter to SEC chair Mary Jo White earlier this week, urging her to start regulating the practice:

Stock buybacks use profits to purchase a company's own stock instead of investing in the worker training, research, or innovation necessary to promote long-term growth. ... In the past, this money went to productive investments in the form of higher wages, research and development, training, or new equipment. Today, cash is being extracted from companies and placed on the sidelines. Buybacks are now undermining the stock market's role in capital formation.

In writing the letter, Baldwin reportedly partnered with a University of Massachusetts, Lowell, researcher named William Lazonick, whose work has also been cited by - you guessed it - Elizabeth Warren.

Here's Sen. Warren referencing Lazonick in a speech about income inequality last year (via the IBT):

But leftist senators are not the only ones talking about buybacks.

Earlier this month, BlackRock CEO Larry Fink sent a letter to all the CEOs of S&P 500 companies, asking them to put an end to stock buybacks and dividend payments.

"Corporate leaders' duty of care and loyalty is not to every investor or trader who owns their companies' shares at any moment in time, but to the company and its long-term owners," wrote Fink, who proposed taxing any investments held for less than three years as regular income instead of at the long-term capital gains rate in order to shift investor focus from short-term to long-term investments.

(Remember that BlackRock tends to hold investments for years  - sometimes decades. So Fink has a direct interest in shifting tax policy to favor longer-term investments.)

Fink and others argue that buybacks are becoming so common (a record $1 trillion was returned to shareholders last year via buybacks and dividends, according to The New York Times) because of shareholder activists who use their clout to bully and push for capital returns.

As for Congress, it's unclear what exactly sparked the sudden interest in buybacks, but for Elizabeth Warren it could prove a more fruitful pursuit - one where she could actually team up with some of Wall Street and the business community - than some of her other recent battles.