Colorado's liquor stores soon expect to open on Sundays, as owners agree to forgo the state-protected day off — a break from their prior position.

The about-face comes as the store owners attempt to stave off another change many consumers have clamored for: wine and full-strength beer on grocery-store shelves.

Lawmakers will consider both plans to loosen Colorado's blue laws during the legislative session, though supermarket sales face stiff opposition from liquor stores worried the competition will kill them.

Both sides — supermarket chains and the liquor industry — say a fight is brewing, and they are lining up powerful offenses.

Sen. Brandon Shaffer, D-Longmont, committed to carrying the yet-to-be-introduced supermarket bill this year, but he said he's looking for ways to lessen the blow to mom-and-pop liquor stores.

"There is a huge disconnect between what we're hearing down here from lobbyists opposing this . . . and what constituents feel is reasonable," Shaffer said.

Colorado is one of 16 states that still abide by the Prohibition-era law banning Sunday sales at liquor stores, according to the Distilled Spirits Council of the United States.

State law also limits supermarkets to selling beer that is no more than 3.2 percent alcohol by weight, or about half the potency of the regular beer sold at liquor stores.

Shaffer's proposal — carried by Rep. Jack Pommer in the House — would lift the limitation for grocers that collect at least 51 percent of their revenue from food sales and also have a pharmacy, according to lobbyists from both sides.

The criteria would shut out big-box stores like Target and corner grocers alike, critics say.

"This is the worst type of special-interest legislation that only benefits out-of-state grocery monopolies," said Scott Chase, a lobbyist for larger liquor stores.

At stake for consumers could be variety on one hand and convenience on the other.

The liquor industry reps warn that chains like Safeway and King Soopers will dominate the booze market, gravitating toward high-volume brands and neglecting local breweries and producers popular in smaller shops.

Grocery-store advocates say shoppers would rather choose their wine with their dinners and point to major cities like Miami that have allowed alcohol in supermarkets without hurting liquor stores.

"Grocers are in the business of responding to consumer demand," said Sean Duffy, spokesman for the Rocky Mountain Food Industry Association, which represents 400 chains, independent stores and wholesalers in Colorado and Wyoming. "While they're buying their dinner, they want to be able to pair up a bottle of wine right there, without another stop."

The proposal has had a sobering effect on Colorado's liquor-store owners, many of whom opened near large grocers.

Just a block from the dome under which lawmakers will decide, the manager of Denver Drug and Liquor says a sudden change in the rules will drive his store out of business.

"It will be a big disaster," said Tekle Hailu, whose small store opened three years ago.

Hailu's is a common complaint, according to Jeff Lim, chairman of the Korean Liquor Retail Association, which played a key role in blocking a Sunday-sales bill in 2005.

His organization is one of many liquor-industry groups — also including craft brewers and wholesalers — lined up against the grocery bill.

Also looming on the horizon is a potential ballot measure to allow supermarket sales — a tack large chains tried unsuccessfully in Massachusetts in 2006.

Shaffer — who's been inundated with calls and e-mails from concerned business people — said the fate of the grocery bill is uncertain.

If nothing else, "it's the start of a conversation," he said.