26 USC 4121 - Imposition of tax

(a) Tax imposed 

(1) In general 
There is hereby imposed on coal from mines located in the United States sold by the producer, a tax equal to the rate per ton determined under subsection (b).
(2) Limitation on tax 
The amount of the tax imposed by paragraph (1) with respect to a ton of coal shall not exceed the applicable percentage (determined under subsection (b)) of the price at which such ton of coal is sold by the producer.
(b) Determination of rates and limitation on tax 
For purposes of subsection (a)

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(1) the rate of tax on coal from underground mines shall be $1.10,
(2) the rate of tax on coal from surface mines shall be $.55, and
(3) the applicable percentage shall be 4.4 percent.
(c) Tax not to apply to lignite 
The tax imposed by subsection (a) shall not apply in the case of lignite.
(d) Definitions 
For purposes of this subchapter
(1) Coal from surface mines 
Coal shall be treated as produced from a surface mine if all of the geological matter above the coal being mined is removed before the coal is extracted from the earth. Coal extracted by auger shall be treated as coal from a surface mine.
(2) Coal from underground mines 
Coal shall be treated as produced from an underground mine if it is not produced from a surface mine.
(3) United States 
The term United States has the meaning given to it by paragraph (1) of section 638.
(4) Ton 
The term ton means 2,000 pounds.
(e) Reduction in amount of tax 

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(1) In general 
Effective with respect to sales after the temporary increase termination date, subsection (b) shall be applied
(A) by substituting $.50 for $1.10,
(B) by substituting $.25 for $.55, and
(C) by substituting 2 percent for 4.4 percent.
(2) Temporary increase termination date 
For purposes of paragraph (1), the temporary increase termination date is the earlier of
(A) January 1, 2014, or
(B) the first January 1 after 1981 as of which there is
(i) no balance of repayable advances made to the Black Lung Disability Trust Fund, and
(ii) no unpaid interest on such advances.