About 1800 cement industry jobs are at risk from Labor’s carbon tax and proposed new shipping rules, the federal opposition says.

Nationals leader Warren Truss says the industry is facing a double whammy under the Gillard government. He says domestic cement manufacturers could be killed off by "dirtier" imports, made cheaper under the carbon tax.

"The paradox is Australian cement production is a leader in low-emission technology and any shift to imports will force global CO2 emissions to rise," Mr Truss said.

Australian cement had the world’s second lowest greenhouse gas emissions behind Japan, he said.

"But the carbon tax will price Australia’s cleaner cement out of the market, giving the green light to our international competitors to boost their higher CO2-emitting production and flood Australia with dirty cement.

"... the Australian cement industry will be crushed by competitors who will not be paying a carbon tax."

Mr Truss said Labor was also rewriting the Navigation Act to force businesses that ship products around Australia to use domestic union-dominated vessels.

He said "unionised shipping" in Australia cost significantly more than current international market rates and would be another blow to the industry.

"Right now it costs about the same to ship cement from China to Australia as it does to ship it from Adelaide to Port Kembla," he said.

"Under the Gillard government’s sop to the maritime union, our biggest competitors in cement - China, Indonesia, Taiwan and Thailand - will dramatically undercut Australian suppliers on shipping costs alone."

The Cement Industry Federation (CIF) backed Mr Truss’s claims, saying the shipping reforms would impose new cost burdens on the sector.

"Australian manufacturing cannot afford adding further cost imposts as a result of regulatory changes to coastal shipping," a CIF spokeswoman said in a statement.

"While improving job security and conditions for Australian-based shipping crew is important, this must be weighed against the job security for manufacturing workers in primary production and manufacturing industries."

Meanwhile, Mr Truss said a large section of the cement manufacturing sector would not be compensated under the carbon tax plan.