Shares in cement manufacturers fell in early trade on Friday after they were fined a combined $1.1 billion for price fixing, even as many of them vowed to appeal the ruling by the nation's increasingly assertive anti-trust regulator.

Eleven of the country's biggest cement companies were handed the record fine by the Competition Commission of India, which found them guilty of colluding to push up prices by underusing their plants and creating artificial shortages.

The bigger-than-expected penalty, seen as a flexing of muscles by the regulator, is likely to be dragged into a legal quagmire as the cement manufacturers prepare to enter an appeals process.

India's three biggest manufacturers UltraTech, ACC and Ambuja Cements said they would appeal the ruling at the country's Competition Appelate Tribunal.

"We have not indulged in any cartelisation," O.P. Puranmalka, head of cement at Ultratech, said in a statement.

Shares in Ultratech were trading 1.5 percent lower at 0415 GMT, compared with a 0.6 percent decline in the broader Mumbai market. ACC shares were down 2.0 percent, while Ambuja was trading 2.5 percent lower.

ACC and Ambuja are controlled by Switzerland's Holcim.

The Indian unit of France's Lafarge SA was also found guilty in the ruling, which came five years after a similar inquiry by the CCI's predecessor accused 44 of India's cement companies of fixing prices.

The fines, equivalent to 50 percent of each company's profit from the fiscal years ending in 2010 and 2011, are payable within 90 days of the ruling.

There is no guarantee that the CCI will force the companies to pay up, however.

Last year the watchdog slapped a 6.3 billion rupees penalty on DLF, India's biggest developer, for abusing its dominant position. DLF is appealing the decision and the next hearing in the case is scheduled for June 27.