(CNN) Massachusetts Democratic Sen. Elizabeth Warren and Vermont independent Sen. Bernie Sanders met Wednesday night as speculation about their plans for the 2020 presidential election heats up, a source familiar with the meeting said.

Only the two senators were at the meeting at Warren's condominium in Washington, according to The New York Times, which was first to report the meeting. Citing two Democrats briefed on their discussion, the Times reported the senators told each other they are seriously considering running for president in 2020.

The source familiar with the meeting told CNN it's "not surprising" that the two would meet, considering their closeness as Senate allies and their respective political ambitions.

Some on the left are concerned that two high-profile progressives running against each other would take away from each other's support, which could lead to a less progressive candidate winning the nomination, according to the Times.

"When it comes to progressives, I think Bernie and Warren are in a different league," California Democratic Rep. Ro Khanna told the Times. He said, "I'll have to decide" who to support if both senators run, according to the Times.

Read More