March 18 (Reuters) - U.S. Steel, whose deal to be

bought by Japan's Nippon Steel ( NISTF ) has run into political

resistance, including from President Joe Biden, forecast

first-quarter earnings below estimates on Monday due to lower

demand in its tubular business.

The company's tubular business produces steel casing and

tubing, line pipes and mechanical tubing, catering to customers

primarily in the oil, gas and petrochemical markets.

"Lower selling prices are expected to negatively impact the

segment's financial performance. Additionally, lower shipment

volumes are anticipated as rig counts remain stagnant and

natural gas demand softens due to a mild winter," U.S. Steel

said.

The company forecast first-quarter adjusted earnings per

share between 80 cents and 84 cents per share, below analysts'

average estimate of 89 cents per share, according to LSEG data.

The weak profit outlook comes at a time when Nippon's

$14.9-billion deal to acquire U.S. Steel has run into opposition

from lawmakers in the United States, who have cited national

security concerns.

The opposition peaked last week, after President Biden said

the company must remain a domestically owned U.S. firm.