On Thursday morning, the senator sent Musk a letter with 30 recommendations for how his DOGE commission could slash $2 trillion in U.S. spending over the next 10 years.

In the letter, Warren suggested several progressive policies, including closing tax loopholes for corporations and the wealthiest earners, renegotiating Department of Defense (DOD) contracts, and allowing Medicare to negotiate lower costs for prescription drugs.

Warren claims in the letter that $200 billion could be preserved by renegotiating defense contracts, pointing to a 2011 report that found contractors regularly hike prices for the military.

Musk has not publicly addressed the letter, and representatives for the billionaire did not return Fortune‘s request for comment.

DOGE’s rocky start

Musk’s Department of Government Efficiency has had a rocky start. The commission has already lost its original co-chair, Vivek Ramaswamy, and has been hit with three lawsuits.

Musk has also backtracked on some of the department’s lofty promises around budget cuts.

In an interview broadcast on X, the billionaire told political strategist Mark Penn the previously promised $2 trillion figure was a “best-case outcome” and that he thought there was only a “good shot” at cutting half that. 

It’s still unclear how exactly Musk intends to slash government spending.

Musk has been soliciting advice from tech leaders on how to root out unnecessary red tape and eliminate waste. However, the main suggestion appears to be a sizable reduction in government headcount.

In an op-ed in the Wall Street Journal, the then DOGE co-chairs said they anticipate “mass headcount reductions across the federal bureaucracy.”

Musk has done similar things at his companies, most notably slashing X’s overall headcount by nearly 80%. The billionaire has also done several rounds of layoffs at Tesla.  

Warren and Musk’s public spats

There’s no love lost between Musk and Warren.

The former law professor and Democrat senator has sparred with Musk over Tesla and X in the past.

In one public spat in late 2021, Warren accused Musk of “freeloading off of everyone else,” while Musk hit back, calling her “Senator Karen.”

Warren has recently expressed concerns about potential conflicts of interest posed by Musk’s proximity to the White House.

In December, the senator wrote to President Trump to ask for conflict-of-interest rules to cover Musk.

“Putting Mr. Musk in a position to influence billions of dollars of government contracts and regulatory enforcement without a stringent conflict of interest agreement in place is an invitation for corruption on a scale not seen in our lifetimes,” she wrote in the letter.

She said that Musk was “no ordinary citizen” but the “CEO of several companies that have significant interests before the federal government,” pointing to Tesla’s government contracts to provide electric vehicles and services to the federal government.