According to a report from The Hill, structured around the leaking of a letter sent by House Intelligence Chairman Devin Nunes to the FBI, “The letter was provided to The Hill from a source in the intelligence community“, outlines a massive amount of unmasking done by Obama officials in 2016.

(Via The Hill) […] “We have found evidence that current and former government officials had easy access to U.S. person information and that it is possible that they used this information to achieve partisan political purposes, including the selective, anonymous leaking of such information,” Nunes wrote in the letter to Coats.
[…]  In Thursday’s letter, Nunes said the total requests for Americans’ names by Obama political aides numbered in the hundreds during Obama’s last year in office and often lacked a specific intelligence community justification. He called the lack of proper justifications a “serious deficiency.”

His letter noted requests from senior government officials, unlike career intelligence analysts, “made remarkably few individualized justifications for access” to the U.S. names.
“The committee has learned that one official, whose position had no apparent intelligence related function, made hundreds of unmasking requests during the final year of the Obama administration,” Nunes wrote. “Of those requests, only one offered a justification that was not boilerplate.”
Sources familiar with the Nunes letter identified the official as then-U.N. Ambassador Samantha Power.
Power did not immediately respond to a request for comment.
Nunes also wrote that “Obama-era officials sought the identities of Trump transition officials within intelligence reports.”  (read more)