The US Defense Department is investigating whether Pentagon employees tried to get the federal government to pay them back the money they spent at gambling casinos and strip clubs, using government-issued credit cards.

In May, the Pentagon’s Inspector General reported that US military personnel spent nearly $1 million at casinos and almost $100,000 at “adult entertainment establishments” using the cards from July 1, 2013 to June 30, 2014.

On Wednesday, the Pentagon’s Inspector General’s office released a memorandum in which the US Senate Armed Services Committee asked for a follow-up investigation on the matter.

“Our objective is to determine whether (Defense Department) cardholders who used government travel cards at casinos and adult entertainment establishments for personal use sought or received reimbursement for the charges,” the Assistant Inspector General Michael Roark told Pentagon officials in the memo.

“In addition, we will determine whether disciplinary actions have been taken in cases of personal use and if the misuse was reported to the appropriate security office,” Roark added.

A Pentagon official said in May that disciplinary action has already been taken in the majority of the cases. The official said the US government did not necessarily pay the charges as card holders pay their own bills, and submit receipts of government-related expenses.

In its report, the Inspector General highlighted one particular case, in which a US Air Force member was demoted after spending $4,686 at a club in Las Vegas, Nevada.

The airman tried to spend another $920, but had already surpassed his credit limit, the report added.

The report also mentioned an unnamed Navy SEAL on official duty in El Paso, Texas, who used his government credit card at a strip club to pay more than $1,000 for services he received during his 17-day stay.

The US Defense Department has handed out government credit cards to 1.6 million people, who are only supposed to use them for official travel-related expenses only.

An audit conducted from July 1, 2013 to June 30, 2014, found that the 20 million transactions made these cardholders racked up a hefty $3.4 billion in expenses.