The Texas 25th US congressional district is not what it used to be. Once a solid Democratic constituency built around Austin, the state's liberal capital, it is now an elongated hodgepodge of urban dwellers, farmers and military families extending 180 miles north to the edge of Fort Worth. And it's about to elect a Republican.

That is by design.

After months of legal battles reaching to the supreme court, Texas is holding elections for the US Congress and state legislature in November based on constituency maps a federal court has described as planned by Republican lawmakers with "discriminatory intent".

Democrats and civil rights groups say the intent is to neutralise a rapid expansion of the Latino vote and rig individual elections in favour of Republican candidates, strengthening the party's hand in the US Congress and helping it maintain a hold on the Texas legislature.

"It's a power grab," said Elaine Henderson, the Democratic candidate for Congress in the newly drawn 25th district. "The Republicans are trying to stave off the inevitable. The Hispanic vote is coming, and it's with us, not them."

Republicans acknowledge that they have carved up districts to dilute the impact of the swelling Latino vote, which leans strong toward the Democrats. But they balk at accusations of racism, saying it's just Texas politics as usual. But civil rights activists say that even if the intent is political, the outcome is racist.

Democrats have told federal courts that the maps "grossly misrepresent the demographics" of Texas and are part of a wider attempt by conservatives in several states to turn back the gains of the civil rights era.

According to the 2010 census, Texas's population grew by 4.2m over the previous decade – a 20% rise. That earned Texas four more seats in Congress at the expense of states in the midwest and north-east.

But the census also showed that the bulk of that increase – 63% – was Latino. That, combined with a significant rise in the number of African Americans and Asians, has for the first time made Texas a "minority-majority" state with a little more than half the population Hispanic, black or Asian.

The increase in the number of white people in Texas was so small that on its own it would not be enough to qualify for a single new seat in Congress. Yet civil rights lawyers say Republican legislators have redrawn electoral maps so that not a single additional Latino or African American will be elected to Congress in Texas, while the Republican party will probably pick up two and possibly three of the new districts. Something similar is happening in elections to the state legislature.

"You cannot responsibly morally or legally respond to the census with the maps the Republicans drew which arguably produce zero new minority seats," said Harold Cook, a Democratic political strategist who in 2003 organised a mass departure of his party's state Senators into neighbouring New Mexico in order to prevent a quorum and block an earlier bid at gerrymandering.

"What the Republicans have been doing is drawing seats so that minorities cannot win them and Republicans are protected from the growing Latino vote. It's not only redistricting. There are voter ID laws, more stringent regulations on registering to vote. It's all about trying to hold off this tide of minority voters that are going to swamp the Republicans in this state. But in the end they won't be able to stop it."

One of the most brazen cases of gerrymandering is the 27th congressional district on the east Texas coast. For 26 years it was held by a Latino and Democrat, Solomon Ortiz.

In 2010, a Tea Party Republican, Blake Farenthold, took the district by just 800 votes as part of the nationwide backlash against Barack Obama that saw rightwing Republicans mobilised while much of the Latino vote stayed at home. Farenthold was almost certain to lose the seat in November, but then the Republican map designers stepped in.

They lopped off a chunk of the south end of the constituency packed with Latino voters, including the border city of Brownsville, and then added a clutch of counties to the north and west around Corpus Christi with a sizeable chunk of white voters.

In doing so, the 27th district went from 70% Latino to less than 50%. The result is that Farenthold is now considered a safe bet for re-election.

Ryan Downton, a Republican lawyer who played a leading role in redrawing the congressional electoral map, admitted that was the intent at a court hearing in January. "We drew Farenthold a more Republican district," he said.

Downton conceded the same intent in manipulating the boundaries of the 23rd district, which runs from San Antonio to El Paso, to favour a Republican incumbent, Francisco Canseco – the party's only Latino congressman from Texas.

A Republican official, who does not wish to be named because of the continuing legal action, acknowledged that boundaries were redrawn for partisan advantage.

"It's a political draw," he said. "I certainly don't think it's undemocratic. There's an element of human nature that says to the victor goes the spoils."

Texas will have 36 seats in the next US Congress. But the number of Latino representatives from the state is likely to remain static at five, the same as in the present 32-seat Texas delegation.

Republicans say that is because Democratic primary voters have chosen white, not Latino, candidates even in districts with a substantial number of Hispanic voters. But Luis Roberto Vera, chief counsel for League of United Latin American Citizens, has argued before the supreme court that it is a result of the way Latino voters have been parcelled out to diminish their impact.

"How do they do it? We call it cracking and packing," he said.

Cracking breaks concentrations of Latino and other minority voters and distributes them among mostly white conservative-leaning districts so they are overwhelmed by Republican voters. But that is not always possible, in which case as many minority voters as possible are packed in to a single district so the impact of their ballots is diminished.

"They draw districts that are packed with minorities – 80 or 90% when all we need to win is 55% – or they spread us out thinly. They crack us up to divide the vote or pack us all together. Whatever they need to do to suppress the Latino vote," said Vera.

For instance, in Austin – a city with a nearly 60% increase in Latinos over the past decade – voters who once lived in one of two congressional districts are now carved up between six, greatly diluting their impact because they have mostly been parcelled off to Republican constituencies where they are overwhelmed by conservative voters. Almost every other US city of similar size, such as Detroit, Memphis and San Francisco, is divided between two congressional districts.

The breaking up of the vote in Austin appears in part to have been aimed at levering a sitting Democrat from office.

The 25th district used to be a safe seat for a Democratic congressman, Lloyd Doggett. But it has virtually been drawn out of existence by the Republican legislature – nine years after a similar move against him was blocked by the courts. Doggett went in search of a more viable seat and fought his way through a primary to contest a district east of Austin, where he is expected to be elected.

Henderson is now struggling against the odds in what was Doggett's old district in name if not geography. She regards the redrawing of the 25th's boundaries as a blatant Republican move to get rid of Doggett because he was popular with Latino voters and influential in Washington.

"I saw the redistricting as a way to divide Austin up enough that even Lloyd wouldn't have his seat anymore. They thought they could redistrict Lloyd out of a seat, the Democrat from the area," she said. "This district is totally new. I don't think it's ever been like this. I think they thought they were making a nice safe district for a Republican out of this."

A Republican official intimately involved in drawing the new electoral maps, who does not wish to be named because of the continuing legal action, acknowledged as much when Henderson's allegation was put to him.

"There are ways to draw maps that could have assured [Doggett's] election," he said.

So does that mean the map was drawn to try and remove Doggett?

"You could certainly draw that inference," he said. "It's not a stretch to believe that."

The Republican official said that while the courts will strike down maps drawn to discriminate against minority voters, they will let stand politically partisan boundaries. He said the accusations of racism are unjustified and that Texas legislatures have a long history of redrawing election boundaries for partisan advantage.

"Nobody likes being called a racist," he said. "We don't have people over there [in the legislature] who are old-school racist."

The new boundaries were also drawn to move facilities such as medical centres and sports grounds to districts under Republican control, and so that some black Democratic members of Congress found their district offices were no longer in their districts.

The Republicans have not had it all their own way. They wanted to take two mostly African American districts in Dallas and merge them into one but were prevented from doing so by a provision of the Voting Rights Act, a piece of civil rights era legislation.

But on the whole the Republicans have got what they wanted after a series of court battles which saw federal judges substantially redraw the state legislature map earlier this year only for the supreme court to order the lower court to redraw it again based on the Texas legislature's original design. However, a federal court has ordered that the map again be revisited after next month's election.

It is a similar picture in the state legislature. Redistricting is expected to give Republicans seven of the nine new seats there, again in the face of demographic changes that suggest movement should be in the other direction. That will help the party retain its majority and continue to gerrymander elections.

The anonymous Republican official involved with drawing up the new maps said they are not discriminatory.

"If you look back at the senate map of 31 seats, when we started Latinos had seven seats. When we finished they had seven seats," he said.

But Vera said that does not take account of the rapid rise in the number of Latinos living in Texas.

Vera acknowledges that part of the reason Republicans can get away with it is the relatively low turnout of Latino voters. Of more than 4 million Hispanic Americans of voting age living in Texas, just 1 million voted in the 2010 elections, whereas much higher proportions of white and African American voters turned out.

"I hate these people that discriminate and they way they do it. But at the same time I realise that it's also our fault. We don't vote. The Republican party knows that when push comes to shove the Latino community votes less than anyone," said Vera.

"As long as we're not voting, that's what gives them the power to do what they do. Redistrictings are done by the groups in power. Every report shows that if the Latino community came our and voted their numbers we could easily control every election in Texas. We'd be the swing vote, the winning vote."