Janet Chan, manager of the legal division at recruiter Michael Page, said she has seen a 20 percent increase in demand for antitrust attorneys over the past 12 to 18 months.

A string of large cross-border deals are expected to need approval from the Ministry of Commerce, which is typically required when the combined companies' annual sales in China exceed 400 million yuan ($64.4 million).

Top 10 overseas M&As by Chinese companies

Law 'will level the playing field'

These include United States-based conglomerate General Electric Co's $16.9 billion bid for the energy business of French engineer Alstom, a deal that has already been revised to deal with the French government's concerns over jobs.

US medical device maker Medtronic Inc's $43 billion purchase of Dublin-based rival Covidien Plc will need the Ministry of Commerce approval just as China is focused on trying to bring down domestic medical costs.

Linklaters in Hong Kong hired Clara Ingen-Housz from US firm Baker and McKenzie last year to bolster its practice. Mayer Brown JSM has hired a new competition associate who will be joining the Hong Kong practice in September.

Other firms looking to expand have their work cut out for them.

"The talent pool for competition specialists in this region is not a deep one," said Mark Jephcott, head of competition for Asia at Herbert Smith Freehills LLP in Hong Kong.

Aside from M&A, joint ventures in China may also need Ministry of Commerce approval. They have also soared with the estimated value of alliances formed in China up 277 percent in 2013 from 2012, according to Thomson Reuters data.

Multinational companies are also turning to antitrust lawyers for advice on other areas of competition law in China such as price-fixing, due to closer regulatory scrutiny.