“Over the Christmas and New Year holidays with my family in California, I enjoyed my first opportunity in years to reflect on the past and my future with an open mind and an open heart,” she said late Wednesday in an official announcement.

“This afternoon, I submitted my resignation to President Obama.”

Solis, who joined the Obama Administration in 2009, was the nation’s 25th secretary of labor and the first Hispanic woman to hold the position.

The Department of Labor is the overseer of the US Mine Safety and Health Administration as well as the Occupational Safety and Health Administration.

Her tenure, while thought to be more aggressively carried than predecessor Elaine Chao, was not without issues in the mining community. But many mine safety advocates criticized her for failing to enact changes to regulation following the Upper Big Branch explosion in West Virginia in 2010.

“Leaving the department is one of the most difficult decisions I have ever made, because I have taken our mission to heart,” Solis said.

President Obama thanked Solis for her service and called her a “critical member” of his economic team.

“Her efforts have helped train workers for the jobs of the future, protect workers’ health and safety and put millions of Americans back to work,” he said.

Solis’ decision comes just days after another key female member of industry issues, US Environmental Protection Agency director Lisa Jackson, also stepped down from her post.

Well-known as one of the coal industry’s least favorite people, Jackson has been at the vanguard of President Obama’s seeming war on coal.

Her resignation will be effective at the completion of the State of the Union address.

Jackson was head of the EPA for four years.

She presided over the introduction of rules that limit the amount of mercury, sulfur dioxide and soot that power stations can emit.

It is these rules that have made it much more costly for electricity utilities to use coal to fire their generators.