(Bloomberg) — Marathon Oil Corp. warned of a “mass layoff” involving more than 500 employees at its Houston headquarters as part of the $17 billion takeover by ConocoPhillips, according to state filings.

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The affected workers “may reasonably expect to experience a permanent loss of employment during the 12-month period” following closure of the transaction, Marathon said in a notice to the the Texas Workforce Commission released on Wednesday.

The date of the layoffs was listed in a state database as May 28, the day before the merger was publicly announced, although the full filing indicates the reductions are in may cases months away.

“There will be a mass layoff at the Houston Facility wherein at least 500 employees will experience an employment loss,” the filing said.

ConocoPhillips expects to make $500 million in cost and capital savings in the first year of the takeover, which is expected to close during the current quarter.

Marathon didn’t respond to a request for comment. A ConocoPhillips spokesperson referred inquiries to Marathon.

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