Democratic presidential hopeful Sen. Bernie Sanders (I-Vt.) on Sunday criticized rival Hillary Clinton's ties to deep-pocketed donors on Wall Street and in the pharmaceutical industry.

"It is obscene that Secretary Clinton keeps going to big-money people to fund her campaign," Sanders said in an interview on CNN's "State of the Union."

The senator added that Clinton "has now raised well over $15 million from Wall Street for her super PAC, and millions more from the fossil fuel industry, and from the drug companies."

The former secretary of state is scheduled to hold a campaign event next month in San Francisco. Clinton is asking for $353,400 for two seats at a table with herself, actor George Clooney and his wife, Amal Clooney.

While Clinton has courted big donors in the Democratic Party, Sanders has done particularly well with small donors. Almost all of the $75 million his campaign raised last year, for example, came from small donors.