Ahead of a planned merger, oil services companies Halliburton and Baker Hughes said they've received anti-trust queries from the Justice Department.

Both companies said they've received "expected" and "standard" requests from the Justice Department related to Halliburton's pending acquisition of rival Baker Hughes.

"Halliburton and Baker Hughes are working cooperatively with the Department of Justice as it conducts its review of the transaction, which remains subject to shareholder and other approvals, as well as customary closing conditions," the companies said in a joint statement Tuesday.

Separately, the two companies are the largest of their kind. Halliburton under the terms of the deal buys all outstanding shares in Baker Hughes for $34.6 billion.

Baker Hughes had initially balked at the deal when it emerged in late 2014. Before ultimately consenting to the deal, Baker Hughes Chairman and Chief Executive Officer Martin Craighead said in November he was advising shareholders against the deal after Halliburton said it would replace the entire board with its own directors.

Both companies are facing pressure from low oil prices, off about 50 percent from their June values despite the early February rally. Oil companies are cutting their exploration and production spending for 2015 because of the weak commodity market.

Last month, services companies Baker Hughes, Halliburton, along with rival Schlumberger, all announced staff reductions. On Tuesday, Halliburton announced plans to lay off up to 6,400 workers.